The left-hander is on the verge of his first 10-win season since 2009, but he has lost three consecutive starts at AT&T Park and has a 10.24 ERA in the last two. Zito (9-8, 4.19 ERA), though, has momentum and history on his side.He did not walk a batter Tuesday for the first time since his season debut four months ago, limiting St. Louis to two runs in 6 2/3 innings of a 4-2 win."He pitched a great game," manager Bruce Bochy said. "He gave up a couple of home runs ... but he didn't let that faze him at all."Facing the Rockies usually hasn't fazed Zito, either. He tossed a four-hit shutout at Coors Field on April 9 and improved to 6-2 with a 2.39 ERA in 18 lifetime appearances against them -- the last loss came in 2008. At home versus Colorado, Zito is 3-1 with a 1.67 ERA in eight starts, striking out 50 in 59 1/3 innings.Zito could get help in extending his mastery of the Rockies from catcher Buster Posey, who is likely to start again for the Giants (62-52) after pinch hitting in the series opener. Posey hit a two-run homer in Saturday's 9-3 win, and he's batting .444 with six homers and 14 RBIs in 10 games this month."I'm comfortable hitting here and see the ball well," said Posey, hitting .443 with nine homers and 32 RBIs since the All-Star break. "The park is big but all the gaps are big, too."Posey is 13 for 33 with three home runs versus the Rockies this season.Despite Saturday's loss, Colorado (41-70) still has a chance to post a winning record on its six-game road swing against the top two teams in the NL West after taking two of three from the Los Angeles Dodgers.To enhance those chances, the Rockies may need Alex White (2-6, 5.75) to overcome the control issues that have plagued him this season. On Tuesday, the right-hander exited after four shutout innings against the Dodgers in an eventual 3-1 victory because he walked five and quickly reached his pitch limit as part of Colorado's four-man rotation."We know what we've got. We've got 75 pitches, and our job is to get as far as we can," said White, who has issued at least four walks in four of his past seven starts.Drew Pomeranz also pitched only four innings Saturday, the major-league leading 33rd time a Rockies starter has lasted four or fewer.White was hit hard by the Giants in losing his only two career starts against them in an 11-day span last September, getting tagged for nine runs and 15 hits in 9 2/3 innings.Carlos Gonzalez, in an 0-for-11 slump over his last four games, is one of the few Rockies to have some success against Zito, going 8 for 23 with a triple and a home run.Rockies outfielder Dexter Fowler is questionable for this game due to back spasms that prevented him from playing Saturday.