Zito (8-15, 5.31 ERA) went 11-13 with a 4.53 ERA for San Francisco last season after signing a $126 million, seven-year contract, and the Giants felt the left-hander would get things turned around this year. That hasn't been the case, as the 2002 AL Cy Young Award winner has continued to regress and leads the majors in defeats.

Tim Lincecum has emerged as San Francisco's ace, and he picked up his team-leading 15th win Wednesday as the Giants (59-74) defeated Colorado 4-1 for their eighth win in 11 games.

In the seventh inning, rookie Pablo Sandoval hit his first career home run to put the Giants ahead, one batter after Bengie Molina hit his 11th homer of the season. Sandoval is batting .372 (16-for-43) with four doubles and four RBIs in 12 games since being called up from the minors.

Zito just about hit rock bottom in his start against the Reds on April 27, as he was reached for eight runs in three innings of a 10-1 defeat. That was Zito's sixth straight loss, after which he was briefly demoted to the bullpen.

Zito went 3-12 with a 5.99 ERA over his first 17 starts but has shown some improvement lately, going 5-3 with a 4.29 ERA in his last nine.

He gave up three runs and four hits in eight innings of a 4-3 victory over San Diego on Saturday, and will be trying to win three consecutive starts for the first time since May 23-June 4, 2007.

"He's worked his way through the tough times and it has made him a better pitcher," San Francisco center fielder Aaron Rowand said.

While Zito's April 27 start seemed to epitomize his season, the same could probably be said for Volquez, who took the ball for the Reds that day. Volquez (15-5, 2.80) allowed one run and five hits with 10 strikeouts to earn the win in his only career start versus San Francisco.

Cincinnati's newfound ace went 7-1 with a 1.33 ERA in his first nine starts en route to an All-Star game selection, and leads the Reds (58-76) in victories.

Volquez gave up three runs and six hits in six innings of a 7-6 loss to Colorado on Saturday, but did not factor in the decision. The right-hander will likely make six or seven more starts and has a chance to win 20 games in his first full season in the majors.

"I think it would be great," Volquez told the team's official Web site. "It would be good for myself and for the team, too. We'd get some more wins."

The Reds, a league-worst 12-26 since the All-Star break, open a nine-game homestand Friday after picking up three wins on their nine-game road trip.

Brandon Phillips was 6-for-36 (.167) with a homer and three RBIs during the trip, and hopes to get back on track against the Giants. He's 6-for-12 with three home runs and seven RBIs in three games versus San Francisco this season.