Matt Carpenter came into the St. Louis Cardinals' Game 3 matchup with the San Francisco Giants to replace Carlos Beltran—who left after the first inning with a knee strain—but he made an impact in his own right almost immediately, hitting a long home run off Matt Cain in his first at-bat of the game to put the Cardinals on top by a score of 2-1 after three innings.
Carpenter is now 5-5 off Cain in his short career, and 2-6 with three RBI in the postseason; he had a pinch-hit RBI in the Cardinals' Wild Card win over the Atlanta Braves.
Carpenter's job all season has been to fill in for aching veterans—he got his big opportunity as Lance Berkman's caddy, and he's found himself at first base and right field on behalf of Carlos Beltran and Allen Craig. In fact, one of the players he filled in for least was David Freese, the injury-prone third baseman for whom he makes a perfect backup.
In Game 3 of the NLCS he found himself, on very short notice, playing right, a position he's been uncomfortable with throughout the regular season. And through one at-bat and a few innings, it's worked out just-about-perfectly.