HOUSTON – Andy Pettitte feels like nothing has come easily for him this season. Fortunately for him, he faced a team on Tuesday that’s struggled even more than he has.

Pettitte pitched six effective innings, Mike Lamb drove in three runs and a wild pitch by Mark Prior led to two runs for the Houston Astros in a 7-2 win over the Chicago Cubs on Tuesday.

“Well, it was a win,” Pettitte said with a relieved smile. “That’s always a good thing.”

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. He also walked four.

“It wasn’t like I cruised through it,” Pettitte said. “It seemed like I had baserunners every inning.”

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.

Pettitte lost his last two starts and took a no-decision in Houston’s 7-4 loss to Kansas City on June 18.

He got into immediate trouble against the Cubs, giving 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.

Manager Phil Garner said plate umpire Jerry Layne wasn’t doing Pettitte any favors.

“He had a tight zone early,” Garner said, “but he kept battling and grinding and he worked through it.”

Pettitte 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.

“You walk a couple and you feel like you get behind in the count too much, then you start to get too aggressive, then you make mistakes to the middle of the plate,” Pettitte said. “There’s a fine line there, especially the way my season’s going.”

But Pettitte never made a mistake as costly as the one Prior made in the sixth inning, with the Astros up 2-1.

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.

Watching from the clubhouse by then, Pettitte got the most run support he’s received since the 9-2 win over the Cubs on June 13.

“It was a blowout, huh?” Pettitte said. “You couldn’t have convinced me after six innings, I can promise you that. It’s nice to break it open late.”

The Cubs lost for the 10th time in 12 games.

Prior (0-4) allowed four runs, three earned, and four hits in six innings. He struck out seven and walked four in his strongest start since coming off the disabled list on June 18.

He 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.

Prior was more upset about that sequence than he was with the wild pitch.

“It’s got to be a mental thing,” Prior said. “I know I can physically do it, but it happens occasionally and I’ve got to work my way through it.”

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.