Matt Carpenter smacked a two-run home run to power reigning World Series champion St. Louis over San Francisco 3-1 on Wednesday to grab the lead in their Major League Baseball playoff series. St. Louis took a 2-1 edge in the best-of-seven National League Championship Series with games four and five in St. Louis on Thursday and Friday. The series winner will face either Detroit or the New York Yankees in the World Series. San Francisco opened the scoring in the third inning when Angel Pagan singled, took third on a double by Marco Scutaro and raced home on a ground out to the shortstop by Pablo Sandoval. But the Cardinals took the lead at 2-1 in the bottom half of the inning on Carpenter’s two-out blast over the right-field wall off a pitch from Giants starter Matt Cain. Carpenter improved to 5-for-5 at the plate against Cain. “He’s a good pitcher. I just go up there and try to find a good pitch to hit,” Carpenter said. “Today was a dream come true.” Carpenter entered the game to replace St. Louis slugger Carlos Beltran, who suffered a left knee strain running the bases. The Cardinals stretched the lead to 3-1 in the seventh inning when David Freese raced home from third on a bases-loaded ground out by Shane Robinson. Just after that, heavy rain began and halted the game for almost 3 1/2 hours, the afternoon game resuming after 10 pm local time. The delay didn’t help the visiting Giants, who went down in order in the eighth and ninth innings.