Matt Carpenter came off the bench and delivered the hit that knocked out Matt Cain and helped St. Louis win again at Busch Stadium.
Carpenter's two-run single highlighted a three-run sixth and the Cardinals extended their home winning streak to seven games in an 8-2 triumph over the San Francisco Giants in the opener of a four-game set.
Jon Jay tallied four hits, two RBI and a run scored for St. Louis, which won its fourth straight overall and sixth in its last seven games.
Jake Westbrook (11-8), a victor in his last four outings and five of his last six home starts, surrendered two runs on seven hits in six innings.
"He did a nice job, was down in the zone," said Cardinals manager Mike Matheny.
Cain (10-5) fanned seven, but allowed five runs on eight hits and two walks in 5 2/3 innings. He is 2-3 with a 4.40 ERA over his last nine starts since tossing a perfect game on June 13.
"I thought he competed well tonight," said Giants manager Bruce Bochy. "Give them credit, that's a good-hitting ball club. He was a hit away from it being a one-run ballgame and he's done and it's a quality start."
Buster Posey cracked a two-out solo homer over the wall in left-center to tie the contest at 2-2 in the sixth, but the Cards countered in the home half after pushing across three.
Matt Holliday laced a leadoff double into the left field corner, moved to third on Carlos Beltran's fly ball and waltzed home when David Freese lifted a sacrifice fly into center.
Consecutive singles by Yadier Molina and Jay, followed by Rafael Furcal's walk, loaded the bases with two away to set the stage for Carpenter, who pinch-hit for Westbrook.
He lined a 1-2 fastball the other way to left, which brought home Molina and Jay for a 5-2 St. Louis advantage.
"He came up in a perfect situation," Matheny said. "It was a great at-bat and a very timely RBI for us."
Freese's run-scoring base hit and Jay's two-run single in the seventh extended the margin to 8-2.
Earlier, Angel Pagan led off the contest by belting a homer to right, but the Cardinals answered by plating a pair in the second.
Beltran began the frame with a homer to right and Furcal's RBI single to center later in the inning gave St. Louis a 2-1 lead.
San Francisco's Hunter Pence went 0-for-4 and is 4-for-26 since being acquired from Philadelphia prior to Tuesday's trade deadline...The Giants were 0-for-3 with runners in scoring position, while St. Louis finished 4-for-10.