Lyle Overbay belted a three-run homer to lift the host Pittsburgh Pirates to their fourth straight victory, 6-4 over the Boston Red Sox on Saturday before the largest crowd in PNC Park history.

Jeff Karstens (5-4) allowed four runs on six hits in 6 2/3 innings and Joel Hanrahan pitched the ninth for his 22nd save as 39,483 were in attendance, including a large contingent of Red Sox fans. Hanrahan struck out Adrian Gonzalez with a runner on first to end the game.

Tim Wakefield (4-3) allowed five runs on seven hits and walked four as Boston lost its fourth straight and fell one-half game behind the New York Yankees for first in the American League East.

Gonzalez, Josh Reddick and Jacoby Ellsbury hit solo homers for the Red Sox.

The Pirates trailed 2-0 early but scored four times in the fourth, highlighted by Overbay’s sixth homer of the season. Karstens added an RBI single.

Pittsburgh made it 5-2 when Dustin Pedroia misplayed a grounder. Boston cut the deficit to 5-4 in the seventh on homers by Reddick and Ellsbury before Garrett Jones added a solo homer in the bottom half to make it 6-4.