Andy Pettitte pitched six effective innings, Mike Lamb drove in three runs and a wild pitch by Mark Prior led to two runs for the Astros in a 7-2 win over the Chicago Cubs on Tuesday.
Pettitte (7-9) allowed seven hits, but only one run, and struck out three to earn his first win since he beat the Cubs on June 13.
Houston relievers Dan Wheeler and Brad Lidge pitched the final three innings to secure the Astros' fourth straight victory, their longest winning streak since mid-June.
Prior (0-4) struck out seven and allowed only four hits, his strongest start since coming off the disabled list on June 18. But his costly mistake came in the sixth inning, blowing open a 2-1 game.
With one out, Preston Wilson doubled to right-center and Morgan Ensberg and Adam Everett drew consecutive walks to load the bases.
Brad Ausmus lined out before the lefty-batting Orlando Palmeiro hit for Pettitte.
With a 1-1 count, Prior's 107th pitch skidded into the dirt and under Michael Barrett's right knee guard.
Wilson slid home as Barrett made a bad throw to Prior covering the plate. The ball bounced toward the Cubs' on-deck circle and Ensberg scored as Prior chased it down. Prior was charged with an error for failing to corral Barrett's throw.
Craig Biggio added a bloop single to right with the bases loaded in the eighth off Glendon Rusch, making his first appearance since returning from the 15-day disabled list on Monday.
Lamb followed with a two-run double to the left-field corner, giving the Astros at least seven runs for the fourth straight game.
The Cubs lost for the 10th time in 12 games.
Unlike Prior, Pettitte's struggles came early. He gave up hard-hit singles to Juan Pierre and Derrek Lee in the first inning and walks to Michael Barrett and Matt Murton in the second.
He had already thrown 35 pitches when Juan Pierre led off the third with a double, reaching base for the 22nd time in his last 23 games. Pierre trotted to third on Neifi Perez's groundout and scored on Lee's single to right.
Prior retired 11 of the first 12 Astros he faced, striking out four. But with two outs in the third, he walked Biggio and grazed Willy Taveras with a pitch.
Lamb and Lance Berkman followed with RBI singles to center.
The Astros got away with a blown rundown in the fourth.
With two outs, Perez doubled off the left-field wall and Lee walked. As Aramis Ramirez batted, Pettitte threw to Lamb at first, catching Lee leaning toward second. Lamb chased Lee halfway down the baseline, then flipped an errant toss to Biggio, who dropped the ball.
Ramirez lined out to end the threat, then pounded his helmet on the turf as Pettitte walked past him to the dugout.