While the Yankees have been comfortably perched atop the American League East for most of the season, the two teams making the biggest jumps in the Power Rankings this week are division rivals Baltimore and Tampa Bay. While the Orioles' run-differential suggests they're more of a pretender than a contender, the Rays may finally be a challenger capable of overtaking the Yankees (at 11 games behind and with an under-.500 record, the Red Sox are too far back at the moment to be considered a serious challenger).

The Rays have now got Evan Longoria and Matt Joyce back from the disabled list, and have won six straight games since Longoria returned. Tampa Bay's rise, though, is due mostly to its pitching and defense, which have combined to post a 1.79 ERA in August.

By going 8-2 in its last 10 games, Tampa Bay has pulled within five games of New York for the division lead and is now on top of the wild card race. The Yankees are still the AL East favorites, but Tampa Bay looks like a serious contender to reach the postseason for the fourth time in five years.

NOTE: All stats are through Sunday, August 12.

Rankings written by Ben Duronio of Fangraphs.com. The system used to rank the teams is based not on the current standings or a gut feeling about team quality, but on how well they've performed at the underlying traits that predict future performance better than wins and losses.

wRC+ is an offensive index where 100 is league average and every point above or below that denotes how far from league average a player's performance has been up to that point. It is adjusted for park and league, so it takes into account the context of a player's surroundings, and allows for comparison of performance from players in different situations and in different times.

MLB Power Rankings
1Washington <a href=Nationals" title="Washington Nationals">
Last Week: 1
WAR Winning Percentage: .619; Current Winning Percentage: .617 WAR Wins: 71; Current Wins: 71
Although the Nationals have been on a very hot streak as of late, winning eight of their last 10 games and extending their NL East lead to 4 1/2 games, their star rookie outfielder Bryce Harper has been seriously struggling. Harper has hit just .173/.273/.260 over his past 28 games and has been worth -0.4 WAR over that time span. The struggles have dropped his wRC+ to just 101, more or less league average, and likely knocked him out of the top of the Rookie of the Year award race. However, his less heralded teammates have continued to keep the offense rolling, and if Harper gets hot again, the rest of the National League is in trouble.
2Texas <a href=Rangers" title="Texas Rangers">
Last Week: 2
WAR Winning Percentage: .606; Current Winning Percentage: .593; WAR Wins: 69; Current Wins: 67
The Rangers are getting hot again and so is Josh Hamilton. Over the past seven games, Hamilton has hit .455 with three home runs, pushing his season total to a career high 32. Even though he has struggled for the past few months, Hamilton still has a .291 batting average for the season and is on pace to have his second-best year overall, behind only his MVP campaign of 2010. His lack of plate discipline means that he's going to have serious slumps, but when he's going right, he's about as dangerous as any hitter in the sport.
3St. Louis <a href=Cardinals" title="St. Louis Cardinals">
Last Week: 3
WAR Winning Percentage: .591; Current Winning Percentage: .539; WAR Wins: 68; Current Wins: 62
The Cardinals are the only NL Central team above .500 over the past 10 games, but they need to have a few more hot stretches if they want to catch the Reds, who now sit seven games ahead of them in first place. Kyle Lohse and Adam Wainwright have impressed over their past few starts, with both netting a 2-0 record and a 2.84 and 1.13 ERA, respectively, over the past two weeks of play. The Cardinals' bats will likely continue to perform well down the stretch, but they need their starters to pitch like this to make a serious move in the NL Central.
4New York Yankees
Last Week: 4
WAR Winning Percentage: .587; Current Winning Percentage: .588; WAR Wins: 67; Current Wins: 67
Eric Chavez and Casey McGehee have provided Joe Girardi with a nice platoon in Alex Rodriguez's absence, with the two combining for three home runs last week. Chavez has been a very important piece for the Yankees all season, with a 128 wRC+ in 216 plate appearances, but he has really gotten it going since Rodriguez's injury. He has hit .368 with four home runs in 13 games since Rodriguez was hit by a pitch on the wrist, as the Yankees have been able to avoid missing a beat at third base.
5Cincinnati Reds
Last Week: 6
WAR Winning Percentage: .550; Current Winning Percentage: .600; WAR Wins: 63; Current Wins: 69
Cincinnati was able to go on a great hot streak after Joey Votto hit the disabled list, but a recent five-game losing streak makes it clear they need their star player back soon. After being on pace for a potential MVP season, Votto is not expected back until late August, so the Reds will have to continue to fight through and hold off the Pirates and Cardinals long enough for Votto to return to the lineup. If they continue to get Cy Young-caliber pitching from Jonny Cueto, they may be able to do just that.
6Arizona <a href=Diamondbacks" title="Arizona Diamondbacks">
Last Week: 5
WAR Winning Percentage: .549; Current Winning Percentage: .504; WAR Wins: 63; Current Wins: 58
At just five games back of first place, the Diamondbacks are one hot streak away from putting serious pressure on the Giants in the NL West. Unexpectedly, Patrick Corbin and Wade Miley have been the team's best starters of late, with both netting ERAs below 2.50 in their past three starts. Miley has been a great story all season and is a front runner for the Rookie of the Year award, but Corbin has been very impressive in his first season as well. The rookie has a 3.41 ERA and 3.34 FIP in 58 innings between the bullpen and rotation this year, and with Ian Kennedy struggling and Daniel Hudson injured, the Diamondbacks couldn't have asked for anything more from Corbin.
7Detroit <a href=Tigers" title="Detroit Tigers">
Last Week: 7
WAR Winning Percentage: .548; Current Winning Percentage: .530; WAR Wins: 63; Current Wins: 61
I'm not sure enough can be said for the type of season Austin Jackson is having atop the Tigers' lineup. He has been a better offensive player than Prince Fielder this season ? 148 wRC+ to 141 ? and has a higher on base percentage than Miguel Cabrera. In fact, in almost 90 fewer plate appearances, Jackson's 4.8 WAR barely trails Cabrera's 4.9 mark. It is certainly feasible to argue that when healthy, Jackson has been Detroit's best position player this season.
8San Francisco Giants
Last Week: 9
WAR Winning Percentage: .546; Current Winning Percentage: .548; WAR Wins: 63; Current Wins: 63
Hunter Pence has really struggled in his transition to San Francisco, but the Giants are still 7-3 in their past 10 games, as they hold a narrow one game lead over the Dodgers in the NL West. In 12 games and 54 plate appearances, Pence has hit just .154/.167/.288 with a 17 wRC+, which are extremely poor numbers for a player of Pence's offensive caliber. San Francisco will need him to start doing what he was acquired to do ? namely, provide Buster Posey and the rest of the lineup some support.
9Boston Red Sox
Last Week: 11
WAR Winning Percentage: .546; Current Winning Percentage: .491; WAR Wins: 63; Current Wins: 57
The good news for the Red Sox is that they are just 5 1/2 games out of the wild card lead and they finally got a good pitching performance from Jon Lester, who stuck out 12 Indians and allowed one run in six innings on Sunday. The bad news is that Boston would have to leap three teams to take a hold of the second wild card and it has gone just 4-6 in its past 10 games. The Sox certainly have the talent to make a late season push, so counting them out of it in mid-August may not be wise.
10Los Angeles <a href=Angels" title="Los Angeles Angels">
Last Week: 8
WAR Winning Percentage: .544; Current Winning Percentage: .522; WAR Wins: 63; Current Wins: 60
Albert Pujols rebounding from a rough start has been a big story for Los Angeles, but now Kendrys Morales is doing so as well, just not quite as impressively as Pujols has. After missing all of 2011 and most of 2010 with injuries, Morales has 15 home runs and a 114 WRC+, including six home runs in his past 14 games. The Angels have had to mix and match their lineup to get everyone enough playing time, but sticking with Morales during the middle stretch of the season when he was struggling certainly looks like it is paying off.
11Atlanta <a href=Braves" title="Atlanta Braves">
Last Week: 10
WAR Winning Percentage: .542; Current Winning Percentage: .522; WAR Wins: 62; Current Wins: 66
The Braves deadline acquisition, Paul Maholm, made his presence felt in a big way in his second start for Atlanta. He threw a complete game shutout and allowed just three hits against the Mets on Friday, as they took two of three in New York this weekend. With Tommy Hanson set to return and the entire rotation pitching well, it seems as though the Braves will go to a six man rotation for the time being, until injury or poor performance forces them to return to a standard five man rotation.
12Tampa Bay Rays
Last Week: 15
WAR Winning Percentage: .537; Current Winning Percentage: .544; WAR Wins: 61; Current Wins: 62
With a lack of offense from both Sean Rodriguez and Elliot Johnson, the Rays have decided to try Ben Zobrist at shortstop this past week. Zobrist's ability to play almost every position on the diamond has helped Tampa Bay extensively in the past, and the Rays are hoping that his flexibility helps them again this season as they try and get as much offense as possible from an infield that has struggled for a majority of the season. Shortstop is not his best position defensively, but it allows Tampa Bay to put Ryan Roberts or Jeff Keppinger at second base in place of the two aforementioned lackluster shortstops.
13Chicago <a href=White Sox" title="Chicago White Sox">
Last Week: 14
WAR Winning Percentage: .520; Current Winning Percentage: .549; WAR Wins: 59; Current Wins: 62
Chicago is doing its best to hold off Detroit in the AL Central, matching the Tigers' 6-4 stretch over the past 10 games backed by a great couple of weeks from A.J. Pierzynski and Kevin Youkilis. The White Sox have gotten solid performances from Jake Peavy, Chris Sale and Jose Quintana in the top portion of the rotation, but need to find some consistency in the back end. In just three starts since being acquired from the Twins, Francisco Liriano has already shown how erratic he can be, with a 5.65 ERA despite striking out over 10 batters per nine innings.
14New York Mets
Last Week: 12
WAR Winning Percentage: .518; Current Winning Percentage: .478; WAR Wins: 60; Current Wins: 55
The Mets are still struggling but R.A. Dickey continues to enjoy a Cy Young-caliber season. The knuckleballer now is tied with Stephen Strasburg for the NL lead in strikeouts and is fourth in the league in ERA. Without much more to play for, Mets fans can at least look forward to Dickey continuing an excellent season and competing for the top pitching award in his league. It would be amazing to see a knuckleballer win the Cy Young during this era of power pitchers.
15Philadelphia <a href=Phillies" title="Philadelphia Phillies">
Last Week: 13
WAR Winning Percentage: .516; Current Winning Percentage: .456; WAR Wins: 59; Current Wins: 52
The Phillies are giving Domonic Brown a shot to play every day to see what they have for next year, and he has impressed with his plate discipline, with five walks and just four strikeouts in 45 plate appearances. The talented outfielder will hit for more power over the course of the season, but the Phillies have to be happy with his plate discipline, which is usually a very good sign of future success.
16Milwaukee <a href=Brewers" title="Milwaukee Brewers">
Last Week: 16
WAR Winning Percentage: .514; Current Winning Percentage: .460; WAR Wins: 58; Current Wins: 52
The two stories keeping Brewers fans interested in the team at this point are rookies Michael Fiers and Jim Henderson. Fiers has recored a 1.80 ERA in 80 innings pitched with an FIP of 2.22, which points to his performance being somewhat sustainable if he can continue to strike out batters at this high of a rate while walking a minuscule 1.80 batters per nine innings. Henderson has taken over closing duties in Milwaukee and has struck out 14.63 batters per nine in his eight innings in the majors. The 29-year-old is in his first stint in the majors, so this elder rookie succeeding after spending so many years in the minors is really a tremendous story.
17Los Angeles Dodgers
Last Week: 18
WAR Winning Percentage: .513; Current Winning Percentage: .539; WAR Wins: 59; Current Wins: 62
Chris Capuano nearly threw a no-hitter on Sunday, allowing just two hits in a complete game shutout of the Marlins. The Dodgers sit just one game behind red-hot San Francisco but they need to do more offensively; they rank 26th in runs scored, and that kind of production won't be good enough to get them into the postseason.
18Pittsburgh Pirates
Last Week: 17
WAR Winning Percentage: .508; Current Winning Percentage: .561; WAR Wins: 58; Current Wins: 64
There may not be a more overlooked player in the league right now than Neil Walker. The second baseman has hit seven home runs and driven in 23 runs in his past 27 games, providing the Pirates with another very productive bat in the middle of the order along with Andrew McCutchen. Seeing James McDonald struggle this much in the second half is disconcerting for Pittsburgh, but their offense has stepped up as their pitching has ran into issues, allowing the Bucs to maintain a playoff-bound pace.
19Oakland <a href=Athletics" title="Oakland Athletics">
Last Week: 20
WAR Winning Percentage: .476; Current Winning Percentage: .535; WAR Wins: 54; Current Wins: 61
Oakland is still just a half-game out of the AL wild card lead, and their righthanded hitters are really starting to get going. Derek Norris hit two home runs last week while Jonny Gomes added another three. Chris Carter has also had a torrid stretch in his first 32 games in the majors this year, with a .400 on base percentage and 10 home runs in 125 plate appearances.
20Baltimore Orioles
Last Week: 23
WAR Winning Percentage: .458; Current Winning Percentage: .539; WAR Wins: 53; Current Wins: 62
The only team within 5 1/2 games of the wild card with a negative run-differential (-41) is Baltimore. Despite that stat and its low rank in overall WAR, somehow the Orioles continue to win games. They have been a statistical anomaly all season, but with a lack of firepower in the rotation it is difficult to see them maintaining their current winning percentage throughout the last month and a half of the season. Calling up rookie infielder Manny Machado, who homered twice on Friday night and again on Sunday could provide enough of a boost to keep their heads above water, however.
21Kansas City <a href=Royals" title="Kansas City Royals">
Last Week: 22
WAR Winning Percentage: .453; Current Winning Percentage: .430; WAR Wins: 52; Current Wins: 49
The three Royals hitters who signed contract extensions over the past two years -- Billy Buter, Alex Gordon and Salvador Perez -- all had great power weeks, which is good for the future of the organization. The trio combined for 10 home runs over Kansas City's past seven games, and both Perez (eight) and Butler (24) have set career highs for the season. While GM Dayton Moore has struggled to build a respectable starting rotation, he has done a good job of finding hitting prospects and getting them under long-term contracts.
22Miami Marlins
Last Week: 19
WAR Winning Percentage: .445; Current Winning Percentage: .452; WAR Wins: 51; Current Wins: 52
Giancarlo Stanton returning from the disabled list is about the only thing the Marlins can hope will bring fans to the stadium the rest of the season. Miami has not hit the attendance marks it had hoped for with a new stadium and a number of new free agents, which could potentially have long-term effects on the franchise. Stanton turning into a superstar and staying healthy will be a key to the Marlins' future, and his two home runs fresh off his recent DL stint show that he has no lingering effects from his knee injury.
23San Diego <a href=Padres" title="San Diego Padres">
Last Week: 25
WAR Winning Percentage: .440; Current Winning Percentage: .440; WAR Wins: 51; Current Wins: 51
The Padres have actually played really good baseball lately, putting together a six-game winning streak before it was snapped by the Pirates on Sunday, and they could be a legitimate spoiler down the stretch. With three fellow NL West teams competing for playoff spots, San Diego has an opportunity to alter the outcome of the division by continuing to play as well as it has. This week, the Padres can do the same to the Braves, whom they play in a three-game set in Atlanta.
24Toronto <a href=Blue Jays" title="Toronto Blue Jays">
Last Week: 21
WAR Winning Percentage: .438; Current Winning Percentage: .474; WAR Wins: 50; Current Wins: 54
Ricky Romero has had a puzzling season. After coming off of a tremendous 2.92 ERA campaign in 2011, his ERA has ballooned to 5.32 this year, but he has gotten it going lately. In his last three starts, he has a 2.70 ERA over 20 innings despite an 0-2 record. With the Jays far out of contention, getting Romero, who is signed through 2015, to be a reliable ace is a focal point for Toronto's future.
25Seattle <a href=Mariners" title="Seattle Mariners">
Last Week: 24
WAR Winning Percentage: .429; Current Winning Percentage: .457; WAR Wins: 50; Current Wins: 53
After putting together a nice couple of weeks, the Mariners have struggled once again and are still hovering around an even run differential. Seattle has a few nice young bats in its lineup (Jesus Montero and Dustin Ackley among them), some of whom have decent upside, so seeing them finish out the season strong could allow the M's to have a season next year like Oakland is having this season. Most notably, watching Montero and Kyle Seager finish out the season should provide a bit more insight into how they can handle major league pitching.
26Colorado <a href=Rockies" title="Colorado Rockies">
Last Week: 26
WAR Winning Percentage: .423; Current Winning Percentage: .366; WAR Wins: 47; Current Wins: 41
Josh Rutledge has continued to hit well in Troy Tulowitzki's absence, as he essentially auditions for a long term role at second base for Colorado. The rookie has hit .327/.342/.626 over his first 26 games in the majors. While the Rockies would certainly like to see a walk rate higher than 2.7 percent to show sustainable on base skills, his power has been phenomenal in the early stage of his career. With Coors Field being such a hitter's park, the Rockies will have to try and hit their way to playoff appearances in the future, and they are hoping Rutledge turns into a vital part of the lineup.
27Cleveland Indians
Last Week: 27
WAR Winning Percentage: .419; Current Winning Percentage: .461; WAR Wins: 48; Current Wins: 53
As bad as the Astros have been, the Indians' collapse may be even more difficult to watch, as they have completely hit a wall after contending in the early parts of the season. Cleveland has won just three of its past 13 games and now have the worst run-differential in the American League at -108. In fact, the Indians are the only AL team with a run-differential worse than -82.
28Minnesota Twins
Last Week: 29
WAR Winning Percentage: .399; Current Winning Percentage: .430; WAR Wins: 45; Current Wins: 49
The Twins have to be happy with the production they have received from two of their free agent acquisitions, Josh Willingham (29 home runs, .919 OPS) and Ryan Doumit (.292 average, 13 home runs). While they are completely out of contention this year, they do have these two under contract through 2014, so if the Twins do contend in the near future these two would likely be key reasons why.
29Chicago <a href=Cubs" title="Chicago Cubs">
Last Week: 28
WAR Winning Percentage: .398; Current Winning Percentage: .389; WAR Wins: 45; Current Wins: 44
The Cubs are going young for the remainder of the year despite their prospects struggling out of the gate. Josh Vitters and Brett Jackson are both batting .150 or below as they start their major league careers, but the Cubs will be patient with the prospects and allow them to learn against major league pitching. This at least provides some interesting baseball for Cubs fans in August and September.
30Houston Astros
Last Week: 30
WAR Winning Percentage: .369; Current Winning Percentage: .328; WAR Wins: 43; Current Wins: 38
With Houston still having two series to play against the Cardinals, Reds, and Pirates, their best hope for the season is to play the role of spoiler. If one of those teams struggles against the woeful Astros, whose 78 losses are seven more than the next-worst total by another team, it could make a rather large difference in the playoff chase.

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