BOSTON -- Carlos Beltran finished a World Series game for the first time, one day after making his debut.

The 16-year veteran singled in a run to help the St. Louis Cardinals even the Series with a 4-2 win over the Boston Red Sox on Thursday night.

Beltran had left the opener after bruising his ribs in the second inning but was back in the starting lineup for Game 2.

He singled in the first inning, then singled again to drive in the final run in the three-run seventh when St. Louis capitalized on fielding blunders by Boston to erase a 2-1 deficit.

"I wanted to be in the lineup. I worked so hard to get to this point," Beltran said. "Somebody would have to kill me in order for me to get out of the lineup.

"When I left the ballpark yesterday, I had very little hope that I was going to be in the lineup. Tomorrow, I know for sure I'm going to wake up feeling sore."

Michael Wacha beat John Lackey in a matchup of present and past rookie sensations, and this time it was the Cardinals' turn to take advantage of sloppy fielding.

David Ortiz put Boston ahead in the sixth inning with a two-run homer just over the Green Monster in left, ending Wacha's scoreless streak at 182/3 innings -- a rookie record for a single postseason.

But then Lackey, who in 2002 with the Angels became the first rookie in 93 years to win a World Series seventh game, faltered in a three-run seventh. St. Louis went ahead when Matt Carpenter hit a sacrifice fly that led to two runs, the second scoring on errors by catcher Jarrod Saltalamacchia and reliever Craig Breslow.

Beltran followed with an RBI single.

Throughout his career, Beltran has displayed an impressive combination of batting, power and speed. In 2,064 regular-season games, he has a .283 batting average, 358 homers and 308 steals. That earned him eight All-Star game selections.

But in 45 postseason games, he had never reached the World Series. Until Wednesday.

Beltran was sent to a hospital for scans Wednesday night after bruising ribs while banging into the right-field fence to rob Ortiz of a grand slam.

Beltran said Thursday he was given painkillers, and he appeared to be wearing protective padding under his jersey.

"Carlos is such a pro," Cardinals manager Mike Matheny said. "He knows how to handle when he doesn't feel completely 100 percent, which he probably hasn't felt since February. But he's the kind of guy that knows how to make the best of what he has."

When the Series resumes Saturday night in St. Louis, Jake Peavy starts for the Red Sox and Joe Kelly for the Cardinals.

"Excited to get home. I know everybody is," Matheny said.

Wacha, a 22-year-old right-hander, was the N.L. championship series MVP. Wacha wasn't quite as sharp in this one, allowing two runs, three hits and four walks in six innings with six strikeouts.

He threw a career-high 114 pitches, and when he reached the dugout after Ortiz's homer, he slammed his glove onto the bench.

Still, the rookie improved to 4-0 with a 1.00 ERA in four outings this postseason, matching the number of regular-season wins he has in his brief career.

"He pitched outstanding," Cardinals catcher Yadier Molina said. "Just one pitch, to a great hitter like Big Papi. We take our hat off to him, but I mean, he pitched good tonight."

The Cardinals' hard-throwing bullpen combined for one-hit relief. Carlos Martinez got six outs, retiring Mike Napoli on an inning-ending pop-up with two on in the eighth. Trevor Rosenthal struck out the side in the ninth for a save, whiffing Daniel Nava with a 99 mph fastball to end it.

All three St. Louis pitchers were 23 or younger.

"It doesn't surprise me. Those guys got talent," Molina said. "Like I said before many times, they're not afraid to pitch."

A night after the Cardinals made three errors in the opener and allowed the Red Sox to romp 8-1, the fielding failures were on the other side.

Lackey, pitching a day after his 35th birthday, walked David Freese with one out in the seventh and Jon Jay singled. Breslow relieved, and the Cardinals pulled off a double steal as pinch-runner Pete Kozma swiped third -- an uncharacteristically aggressive move for the Cardinals, who ranked last in the N.L. with 45 stolen bases this year.

Daniel Descalso, who started at shortstop after Kozma made two errors in the opener, loaded the bases with a walk. Carpenter followed with a fly to medium left, and Jonny Gomes' throw home was slightly to the first-base side of the plate as Kozma scored the tying run.

Saltalamacchia allowed the throw to glance off his glove as Jay took off for third. Backing up the plate, Breslow was slow to throw and then sailed the ball over shortstop Stephen Drew covering third. The ball bounced into the stands as Jay came home with the go-ahead run.

"I'm sure Craig would like to have that ball back and hold it with a chance to shut down the inning right there," Red Sox manager John Farrell said. "Uncharacteristic of the way I think we've taken care of the baseball this year."