BOSTON -- Two pitchers who signed big contracts before last season, but are now experiencing completely different results, go against each other Thursday at Fenway Park.

Rick Porcello, who signed an $82.5 million extension before ever throwing a pitch for the Boston Red Sox and James Shields, he of the four-year, $75 million contract with the San Diego Padres and now with the Chicago White Sox, close the four-game series in the matinee affair, as the White Sox look for the four-game road sweep, which would be their first four-gamer at Fenway since 1927.

Porcello, who struggled last season, is pitching well. Very well.

Shields, 13-7 with San Diego last year, is not. To say the least.

"He's trying to figure it out right now," White Sox manager Robin Ventura said before Wednesday night's game. "For him, you got a guy who's been around for a while that's had a couple tough starts. For him, it's just getting through it and keep grinding through it."

A couple tough starts? Bombed in his final start with the Padres, who had to eat a chunk of money to trade Shields back to the American League, Shields has three dreadful starts with the White Sox, who added him for stability in their rotation behind Chris Sale.

In the four starts, Shields has allowed 32 hits, 31 earned runs and seven home runs -- in just 9 1/3 total innings.

Acknowledging his new pitcher might be trying too hard with his fourth team, Ventura said, "He's a proud guy. I think this is all new to him."

Red Sox manager John Farrell and some of his hitters know Shields well. David Ortiz is 18-for-60 (.300) with three homers and 16 RBIs and Dustin Pedroia 17-for-58 (.293) with two homers against the right-hander.

"Strong competitor," Red Sox manager John Farrell said when asked about Shields. "A put-away changeup. A guy that was, I think, thrived on the bigger stage or in the spotlight.

"We don't take anything for granted. Yeah, he's had a rough go of his time coming back to the American League, but he's still very capable of making quality pitches."

Shields is just 9-13 with a 4.37 ERA lifetime against the Red Sox -- 2-9 with a 5.42 at Fenway Park. Now, he's trying to both straighten himself out and give his team a win that would put the White Sox, once 23-10 before hitting hard times, back over the .500 mark.

Porcello had a string of four straight no-decision snapped with a win over the Seattle Mariners his last time out. That was his eighth win of the year and now he has to play stopper.

He is 10-8 with a 4.09 ERA lifetime in 21 career starts against the White Sox, much of that compiled while pitching in the same division with the Detroit Tigers.

Porcello enters this game 6-0 in six Fenway starts this season -- making him the 10th Red Sox pitcher since 1913 to open a season with six straight wins at the old ballpark.

Before play on Wednesday, Porcello was tied for fourth in the American League in wins, sixth in walks per nine innings (1.93), eighth in strikeout to walk ratio (4.65) and ninth in WHIP (1.09).

Chicago's Melky Cabrera, a Wednesday night hero with four hits and four RBIs, has owned Porcello, going 14-for-25 for a .560 average, while Avisail Garcia is 7-for-18 (.389).

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