Boston, MA (Sports Network) - Kevin Youkilis blasted a game-winning two-run homer off Mike Parisi in the bottom of the 13th inning as Boston downed St. Louis, 5-3, to avoid a sweep in the finale of a three-game interleague set at Fenway Park.

Mike Lowell greeted Parisi (0-3) by ripping a single of the famed Green Monster before Youkilis, who also homered in the seventh inning, drilled an inside fastball over the Monster in left-center.

"I knew I hit it really well and I thought it would get out but you never know here sometimes, especially in left-center field," Youkilis said. "It felt good off the bat. I just hoped Mikey was running as hard as he could in case it didn't get out but I thought I hit it well enough that it would."

Dustin Pedroia finished 4-for-5 with a run scored for the Red Sox, who have won three of their past five games and now lead the AL East by 1 1/2 games.

Jon Lester allowed two runs on nine hits in 7 1/3 innings but was long gone by the finish. Javier Lopez (2-0) earned the win by recording two outs a scoreless 13th.

Aaron Miles was 5-of-6 for the Cardinals, who have dropped four of six games. Adam Kennedy, who entered the game as a pinch hitter in the ninth, was 3-for-3 with an RBI.

Joel Pineiro started on the hill surrendered just two runs on seven hits in seven-plus innings.

The Cardinals broke a scoreless tie in the sixth when Brendan Ryan and Brian Barton led off the frame by rapping consecutive doubles off Lester. After Barton swiped third with one down, Ryan Ludwick came through with an RBI single to left that made it a 2-0 game.

The Red Sox closed the gap in the seventh after Youkilis touched Pineiro for a two-out solo homer, his 12th on the year.

Boston jumped in front thanks in part to the shaky defense of Rick Ankiel. The center fielder overran a Coco Crisp fly ball, turning it into a triple and Lugo followed with a sacrifice fly to deadlock the game. After Jacoby Ellsbury grounded out, Pedroia kept the inning alive with a single to right.

The diminutive second baseman then swiped second before Chris Perez, inexplicably, lost his command. The right-hander issued three consecutive walks, to J.D. Drew, Manny Ramirez and Lowell to put the Red Sox on top, 3-2, for the first time.

Jonathan Papelbon looked like he was about to close things out for the BoSox when he began the ninth by fanning Ankiel and Yadier Molina. But, pinch hitter Chris Duncan worked a walk before Kennedy ripped a run-scoring double over the head off Crisp in center to even things at three.

The Red Sox had plenty of chances to win things from there and had a runner at third with just one out in both the 10th and 11th innings but couldn't push anyone across.

St. Louis almost forged ahead in the 13th but Duncan was gunned down at the plate by Drew while trying to score on a Kennedy single.

"Just a hellacious game," gushed Cardinals manager Tony LaRussa. "It's one of those things that makes you enjoy this level of competition. Both clubs had chances for a lot of heroics to get something going. A lot of heroics to stop them. What a great competition."