(Reuters) - The St Louis Cardinals, powered by back-up player Matt Carpenter, beat the San Francisco Giants 3-1 in a rain-delayed Game Three on Wednesday to seize a 2-1 lead in the best-of-seven National League Championship Series.

Carpenter, who replaced injured outfielder Carlos Beltran, cracked a two-run home run in the third off Giants starter Matt Cain to give St. Louis a 2-1 lead and send the Cardinals on their way.

"I just go up there and battle and try to get a good pitch to hit, and today I was fortunate to get one of those," said Carpenter, who improved to 5-for-5 against Cain.

St. Louis added another run in the seventh inning when they knocked Cain out of the game just before a storm created a three and a half hour delay.

Closer Jason Motte came on in the eighth and turned in a two-inning save to preserve the win for Cardinals starter Kyle Lohse, who gave up seven hits and five walks in five and two-thirds innings but held San Francisco to one run.

"They put some good at-bats on me, didn't leave the strike zone too much," Lohse said. "They did a good job of getting guys on base and I had to do a better job of keeping them from scoring."

The Giants stranded 11 men on base.

BAD START

Things did not look good at the start for the Cardinals.

First lead-off man Jon Jay was hit by a pitch on his right knee by Cain, perhaps as retaliation for the hard slide in Game One by Matt Holliday on Giants second baseman Marco Scutaro, who missed the next game due to a sore hip and knee.

Then the baserunner was erased when Beltran bounced into a double play and strained his knee trying to beat the throw to first, which turned out that might have been just the lucky break the Cards needed.

After Jay blooped a two-out single in the third, Carpenter smashed his long home run.

The big home run was especially sweet as his Texas-based parents had left home at 2 a.m. and drove nine and a half hours to come to the game.

"It's awesome," Carpenter said. "My dad is the reason I've made it this far in my career. To have him be here tonight to see that, was a lot of fun. This is one of those goals we accomplished together. Today was a dream come true."

San Francisco got on the scoreboard first with a run in the top of the third when Angel Pagan singled, went to third on Scutaro's double and scored on Pedro Sandoval's ground-out.

In what became a theme of the game, San Francisco failed to take further advantage of opportunity when Hunter Pence grounded into an inning-ending double play.

The third run for St. Louis came when a ground ball from Shane Robinson, the Cards' third right-fielder of the game, drove in Brandon Belt.

Game Four of the series will be played in St. Louis on Thursday with Adam Wainwright scheduled to start for the World Series champion Cardinals against 2010 World Series winner Tim Lincecum of the Giants.