ST. LOUIS -- The ball came off pinch-hitter Buster Posey's bat with an arc that suggested a go-ahead, two-out, two-run homer in the top of the ninth inning.

In the St. Louis Cardinals' dugout, pitching coach Derek Lilliquist turned to manager Mike Matheny, unworried as center fielder Peter Bourjos sped to the wall in deep right-center field.

"Derek said, 'That's not a problem.' So I was convinced it was staying in the ballpark," Matheny said before laughing.

Posey's fly ball made it to the wall, but Bourjos ran it down and St. Louis escaped with a 2-1 win over the San Francisco Giants Monday night at Busch Stadium.

On a day where they put one outfielder on the disabled list and may have lost another one with an injury, the Cardinals (76-42) tied a season high by going 34 games over .500 while increasing their National League Central lead over Pittsburgh to six games.

The winning run scored in unusual fashion as first baseman Mark Reynolds reached safely on a fielder's choice in the eighth when shortstop Brandon Crawford threw wide of first while attempting to complete a 6-3 double play.

It appeared that Crawford could have flipped to second baseman Kelby Tomlinson at the bag, but he hurried to second himelf, tagged the bag and spun away from it. The inaccurate throw enabled right fielder Stephen Piscotty to plate the tie-breaking tally.

"He's the best in the game, I think," San Francisco manager Bruce Bochy said of Crawford. "The throw just got away from him, pretty simple. The hitter hit it at the right guy. That's who we want it hit to. I'll take that every time."

Piscotty lashed a one-out triple off reliever Hunter Strickland (2-2), taking advantage of an aggressive route by center fielder Gregor Blanco, who tried to make a running catch in deep right-center and barely missed.

Left fielder Brandon Moss drew an intentional walk, setting the stage for the game-winning sequence.

"That was a tough at-bat by Mark," Matheny said. "He fouled off a really tough pitch right before that. Brandon went hard into second and we got the winning run out of it."

Reliever Kevin Siegrist (4-0) picked up the win, while Trevor Rosenthal survived the scare from Posey to notch his 37th save in 39 opportunities.

Already playing without starting left fielder Matt Holliday (right quad) for the second time this year, the Cardinals absorbed more injury hits in the outfield before and during the game.

Rookie of the Year candidate Randal Grichuk went on the 15-day disabled list with a right elbow strain, and center fielder Jason Heyward departed after two innings with tightness in his left hamstring.

St. Louis still managed a 1-0 lead in the fourth when catcher Yadier Molina yanked a 403-foot homer into the third deck in left field, his third long ball of the year. But the Cardinals stranded nine men in the first five innings.

The Giants equalized in the sixth when Crawford laced a two-out RBI double off starter Michael Wacha, plating third baseman Matt Duffy.

Wacha failed to become the first 15-game winner in the majors despite a good outing. He worked seven innings, allowing six hits and a run with one walk and six strikeouts.

San Francisco starter Chris Heston battled control problems in his 4 2/3 innings, allowing five walks and four hits with a run and four strikeouts. Heston threw 104 pitches before Bochy lifted him.

Minutes after the Giants (64-54) dropped three games behind the idle Los Angeles Dodgers in the NL West and four games behind the idle Chicago Cubs for the second wild-card spot, Posey lamented his near-miss.

"I hit it good," he said, "but I hit it too high."

NOTES: St. Louis OF Randal Grichuk (right elbow) was placed on the 15-day disabled list Monday after leaving Sunday's game before the eighth inning. Grichuk is batting .284 with 15 homers and 44 RBIs in 85 games. ... The Cardinals recalled OF Tommy Pham from Triple-A Memphis to replace Grichuk. Pham appeared in 13 games for St. Louis last month, batting .182 and socking his first homer. ... San Francisco activated C Andrew Susac (right thumb) from the 15-day DL and inserted him into the lineup to give Buster Posey a night off. The Giants optioned C Hector Sanchez to Triple-A Sacramento.