Report Card: John Isner delivers again; Serena Williams shows dominant form

John Isner has led the United States into the Davis Cup semifinals. (Remy de la Mauviniere/AP)

The Report Card hands out grades for the best and worst from the week in tennis. This week, we focus on the Davis Cup quarterfinals and the Family Circle Cup, where Serena Williams won the title in impressive fashion.

John Isner: A-plus. It's one thing to flourish in your individual career; it's another thing to do it at Davis Cup, a format that can make even the strongest and most talented competitors wilt. Isner seems to relish anchoring the U.S. team. He did it again over the weekend with convincing victories against France's Jo-Wilfried Tsonga and Gilles Simon, leading the United States into the semifinals against defending champion Spain in September. The former University of Georgia star is a great testament to how college tennis can forge competitors who can handle the pressure of having your teammates and coach counting on you.

Jim Courier: A. Let's just start calling him "The John Whisperer." Captain Courier just seems to know what it takes to get the best from Isner, who, of course, also knocked off Roger Federer in Davis Cup play this year. Courier also handled the last-minute shuffle resulting from Mardy Fish's unexpected withdrawal perfectly. Instead of scrambling to try to get Andy Roddick or Sam Querrey to travel to France, Courier gave 19-year-old Ryan Harrison a chance at his first live rubber. The eager Harrison may have lost, but Courier's decision to invest in the future will pay dividends down the road.

The Bryan brothers: A. Singles players get most of the glory, but a lot of Davis Cup ties turn on the doubles point. That was the case for the U.S. team in Monaco: Isner got the glory, but it was Mike and Bob Bryan who paved the way to victory by taking care of business against the quality team of Michael Llodra/Julien Benneteau on Saturday, putting the Americans ahead 2-1 heading into Sunday's reverse singles.

Serena Williams: A-plus. While Billie Jean King and the rest of the WTA Original 9 watched, Williams won her 40th career title at the 40th anniversary of the Family Circle Cup in Charleston, S.C. Serena dropped a combined three games in the semifinals (against Samantha Stosur) and final (against Lucie Safarova) en route to joining sister Venus and Kim Clijsters as the only active players with at least 40 titles. Some say that if she plays like she did in Charleston, where she won her first clay-court title since 2008, Serena has a shot at the French Open. I say if she plays like that, Serena has a shot at never losing another match. That sound you hear is the first shot fired in the 2012 clay-court season.

Lucie Safarova: A. Safarova may have taken only one game off Serena in the Charleston final (it's OK, Lucie, the reigning U.S. Open champion got only two), but it was a strong week for the Czech. She defeated Polona Hercog 6-0, 6-0 in the semifinals and scored quality wins over Vera Zvonareva and Aleksandra Wozniak, a performance that moved her from 26th to 23rd in this week's rankings. She also got her first doubles title, pairing with Anastasia Pavlyuchenkova to upset top-seeded Liezel Huber and Lisa Raymond and third-seeded Elena Vesnina and Sania Mirza during the week.

Juan Martin del Potro: B-plus. The Argentine had a good weekend in Buenos Aires. He fought off illness to beat Ivo Karlovic in straight sets on Friday and then sealed the tie against Croatia with a straight-set win over Marin Cilic on Sunday. Granted, Cilic was physically drained by then after playing marathon matches the previous two days, but as a guy who's still proving himself in this pressure-packed competition, Del Potro needed this.

Venus Williams: B-plus. Another week, another solid outing for Venus, who won three more matches in Charleston and raised her ranking from 87th to 71st. The good news for her is that she didn't hit a physical wall like she did in Miami, and she looked fairly comfortable on the green clay. Her three-set quarterfinal loss to Samantha Stosur highlighted her inconsistency, but that's to be expected as she works her way back from an autoimmune disorder. Her best performance of the week, though? Showing up to a banquet honoring the Original 9 a few hours after her tough loss. Classy.

Marin Cilic and David Nalbandian: B. These two Davis Cup opponents definitely get an "A" for effort. Their singles and doubles matches, totaling 10-plus hours, brought the most drama of the weekend, for better and worse. They combined for 241 unforced errors in a five-hour, nine-minute singles match in which Cilic prevailed 5-7, 6-4, 4-6, 7-6 (2), 6-3. With Cilic's relatively surprising win, Argentine captain Martin Jaite's decision to play Nalbandian instead of Juan Monaco on Day 1 was looking like a bad one. But always the Davis Cup warrior, Nalbandian was able to recover the next day and win the doubles rubber with Eduardo Schwank, outlasting Cilic and Karlovic 4-6, 6-7 (6), 6-3, 6-7 (6), 8-6 in four hours and 59 minutes.

Ryan Harrison: B. He took a set off Tsonga but eventually lost 7-5, 6-2, 2-6, 6-2. Not too bad for Harrison's first live Davis Cup rubber. Courier's confidence in him has to be a boost.

Vera Zvonareva and Jelena Jankovic: D. They say it's not the fall that kills you, it's the landing. Though their rankings may not reveal it quite yet, these two are reeling. Jankovic, a former No. 1 who is ranked 20th, has lost her opening match in three consecutive tournaments, failing to win a set and getting bageled twice. The 10th-ranked Zvonareva, an ex-No. 2, hasn't beaten anyone inside the top 50 all year. Get thee a coach before you hit the ground.

Radek Stepanek's alleged behavior: F. After their dramatic five-set Davis Cup match Friday, a victorious Janko Tipsarevic of Serbia accused the Czech Republic's Stepanek of calling him a derogatory name and giving him some version of a handshake that translates into "a middle finger." If Tipsarevic's allegations are true, the ITF should discipline Stepanek. His apparent crass sportsmanship derailed what was otherwise a well-contested tie, which the Czechs won thanks in part to Stepanek's doubles victory with Tomas Berdych on Saturday.

Charleston: A