Jake Peavy was brought in to help San Francisco reach the postseason, and his first start for the Giants could return them to first place in the NL West.
A day after coming over in a trade, Peavy will try to help the Giants halt their three-game slide and overtake the division-leading Dodgers on Sunday night.
With Matt Cain's return from right elbow inflammation unclear, San Francisco (57-47) acquired Peavy from Boston in exchange for two minor league pitchers on Saturday to help fortify a rotation that owns a 3.67 ERA.
"The impetus to execute the trade was accelerated by the news we got about Matt Cain becoming more and more tenuous," general manager Brian Sabean said.
The move reunites Peavy - a World Series champion with the Red Sox last year - with manager Bruce Bochy after they spent 2002-06 together in San Diego.
"I've always admired how he plays the game. He's all-out, full-bore in everything he does. He's a guy you want on your club," Bochy told MLB's official website. "I'm excited about having Jake here and I know he's excited about coming back to the National League and this division."
That familiarity may be welcome for Peavy - the 2007 NL Cy Young winner with the Padres - after going 1-9 with a 4.72 ERA in 20 starts for Boston. Run support was a major issue for the right-hander, who was backed by two or fewer in each of his last eight outings, compiling an 0-6 record with a 4.71 ERA.
That problem may not change with the Giants, who are batting .158 while scoring two runs during a three-game losing streak after being two-hit by Clayton Kershaw in Saturday's 5-0 defeat to Los Angeles (58-47).
The loss dropped San Francisco out of first, one-half game back of the Dodgers.
Peavy can go a long way to changing that since he's 14-2 with a 2.21 ERA in 25 career starts against them. He tossed a three-hitter in an 8-1 road win for Boston on Aug. 25.
That's one reason the Dodgers aren't getting too comfortable atop the West.
"You don't take for granted being in first place," Kershaw said. "We know those guys will be right there with us to the end. We know we have to win a few more games to stay in first."
Having perhaps the best rotation in baseball surely helps their chances of creating some breathing room.
Dodgers starters have a 3.14 ERA to tie Oakland for the lowest in the majors, and Hyun-jin Ryu (11-5, 3.39) has won three straight starts at AT&T Park behind a 1.31 ERA.
The left-hander yielded four hits in seven scoreless innings of a 2-1 win there April 17, and he's 7-2 with a 2.73 ERA in 10 road games on the season.
Ryu again won away from home Monday, allowing two runs in seven innings in a 5-2 victory at Pittsburgh. It was the first time he pitched since allowing two hits in six innings of a 1-0 win at San Diego on July 13, the final game before the All-star break.
"Any time we give him extra rest, he's obviously better," manager Don Mattingly told MLB's official website.
Ryu is 10-2 with a 2.68 ERA on five days' rest in his two major league seasons.
Adrian Gonzalez is 10 for 19 with four doubles, one homer and seven RBIs in the last five games. He doubled on two of his three hits Saturday, driving in a run. The first baseman is 4 for 11 with two homers versus Peavy, including a solo shot last year.