ST. LOUIS -- Manager Mike Matheny knew the numbers, but he nevertheless opted not to tinker with a lineup that has been successfully static all postseason long. And so Matt Carpenter, 4-for-4 lifetime against Giants starter Matt Cain, began Wednesday's National League Championship Series Game 3 back on the bench.

Carpenter hardly had time to get settled in as a spectator.

A first-inning knee injury to Carlos Beltran thrust Carpenter into the No. 2 spot in the lineup, from where he delivered a go-ahead home run that the Cardinals rode to a 3-1 win over San Francisco. The victory -- which came in front of a sellout crowd at Busch Stadium and included a three-hour, 28-minute rain interruption -- put the Cards up, 2-1, in the best-of-seven series.

Since 1985, 17 of the 21 teams to take a 2-1 lead in the NLCS have gone on to advance to the World Series.

"It was huge, especially coming home," said Kyle Lohse, who, despite pitching with only so-so command, earned his second win of the postseason. "We have to take care of business at home, and we did today."

Carpenter, who hadn't taken an at-bat since the NL Division Series, took Beltran's place in right field in the top of the second, just minutes after Beltran felt something catch in his knee as he grounded into a double play in the bottom of the first. It was announced shortly after that Beltran had suffered a left knee strain. A postgame MRI revealed that Beltran is day to day.

Carpenter, unaware that Beltran was even hurting, had no time to prepare for his entrance.

"Next thing you know, Mike [Matheny] came up to me and told me to grab my glove," Carpenter said. "I was in the game before I really had time to think about it."

An inning later, Carpenter took his first at-bat, stepping up against Cain with Jon Jay on base following a two-out single. Cain jumped in front, 0-2, before Carpenter worked the count even. He then drilled a slider 421 feet over the fence in right.

"It didn't have the bite on it that he wanted," catcher Buster Posey said of the fateful pitch.

It was Carpenter's first career postseason home run and one that staked the Cardinals to a lead that would hold for the rest of the night.

"Matt Carpenter showed what type of guy he was today, unfazed," David Freese said. "The guys that have been around here all year know that the guy just steps in no matter what position, no matter where he's hitting, and gets it done."

The biggest hit of Carpenter's budding career also came with his family in the stands, as his parents, Rick and Tammie, joined his wife, Mackenzie, at Busch Stadium by driving through the night from their home in Texas.

"When guys get hurt, especially a guy like Carlos, sometimes that can be kind of a letdown from an energy standpoint as a team," Carpenter said. "I wanted to do something that would bring some life back."

Though Cain was the sharper of the two starters, Lohse outdueled him by maneuvering masterfully through jams. Lohse walked a season-high five and gave up seven hits in a 5 2/3-inning performance that didn't match the efficiency of his last postseason start.

But a pair of double plays and a scuffling Hunter Pence helped Lohse get out of much of the trouble.

"I thought it was a classic Kyle Lohse, just pitching," Matheny said. "Kyle Lohse, from the opening day of the season, has been such a steady starter for us and does a great job of figuring out how to get outs, even when he doesn't have his best stuff."

Consider Wednesday Exhibit A.

Lohse stranded three in the first two innings before the Giants scored a third-inning run. Poised for a much bigger inning, San Francisco gave Lohse a hand in escaping without any additional damage. After Lohse threw six straight balls, Pence, with runners on the corners, swung at a 2-0 pitch and grounded into an inning-ending double play.

Lohse left two more runners in scoring position in the fourth and retired Pence to end another threat in the fifth. The bullpen then picked up where Lohse left off, sealing the Giants' defeat, in which they went 0-for-7 with runners in scoring position and stranded 11.

"When you have a game like that, 100 [pitches] feels like 200," Lohse said of his 108-pitch effort. "It was tough. I couldn't take a pitch off. I couldn't lose my concentration at all. Any one of those guys could have gotten me with guys on base and it changes the whole game."

Trevor Rosenthal closed the sixth with two on. Mitchell Boggs assisted Edward Mujica by stranding another two with back-to-back strikeouts in the seventh.

Matheny brought in Boggs as part of a double-switch that also inserted Shane Robinson. Robinson's spot in the batting order came up in a critical spot in the bottom of the frame, too, and, with the bases loaded, he put a ball in play to add the insurance run with a forceout.

That meant all three St. Louis runs were driven in by the team's reserve position players, a group that had combined for one hit and two RBIs in the team's first eight postseason games.

"When you're not playing every day, you don't get too many opportunities to capitalize on," Robinson said. "You have to constantly be in the game at all times. It's mentally draining, but our coaches do a good job preparing us to get loose during the game and knowing the situations that possibly could come up."

The rain delay followed, after which closer Jason Motte entered for the rare two-inning save opportunity. Matheny gave him a little more than 30 minutes to prepare for what would be the first six-out save of his career.

Motte opened with a nine-pitch eighth, situated himself next to a heater to keep his arm warm for a half-inning and then returned to finish off a second 1-2-3 frame. Motte collected the six outs with only 19 pitches, 16 of which were strikes.

"It's a big win," Motte said. "To come here and get the win tonight is big. But this is a good ballclub, so we have to come out tomorrow and do everything we can to try and win that one."