HOUSTON -- Brandon Backe has lost some velocity on his fastball since coming back from a sprained right elbow.
Making his fourth start since coming off the disabled list, Backe (3-1) allowed three hits, walked four and struck out two to improve to 12-3 at Minute Maid Park.
"I know what I've got. I can't get any more than what I've been showing," Backe said. "There's not going to be any 93 mph fastball I'm going to be able to throw by people. I've just got to use my ability to locate it as well as possible. There's no overpowering anybody anymore."
Craig Biggio homered and Adam Everett added an RBI double for the defending NL champions, who have won five of six. They won for only the third time in their last 10 home games.
Dan Wheeler pitched a scoreless eighth, his 10th consecutive appearance without allowing a run, and Brad Lidge struck out all three batters in the ninth to earn his 25th save in 29 chances.
Lidge has struggled at times this season, but looked like his old self on Tuesday, needing just 10 pitches to finish off the Pirates.
"That's the biggest problem for me is that I haven't been able to do it consistently," Lidge said. "I know it will come at some point and I hope this is the start of it."
Jose Castillo hit a sacrifice fly for the Pirates. Pittsburgh has lost five of its last seven and scored two runs or fewer in four of those losses.
Pirates starter Paul Maholm (4-10) allowed five hits, walked four and struck out six in six innings, losing for the third time in seven starts.
Maholm's strikeout total was his highest since he fanned seven in San Francisco on June 11. But he had control problems in the first inning, walking three Astros to load the bases.
With one out, Preston Wilson grounded to shortstop Jack Wilson, who flipped to Castillo to start a double-play try. But Wilson was safe when first baseman Xavier Nady couldn't catch Castillo's off-balance relay throw, and Biggio scored for a 1-0 lead.
Biggio got Houston's first hit in the third, driving a 3-1 pitch from Maholm into the first row of seats in left field. It was Biggio's 15th homer this season and the 275th of his career.
Pittsburgh manager Jim Tracy liked what he saw from Maholm after the rocky start.
"Our starting pitcher did something I don't think we would've seen earlier in the year," Tracy said. "This time, he had another rough start, but he maintained his composure. It was impressive to see him rectify himself the way he did."
Backe didn't allow a hit in the first three innings, but walked three. Jason Bay and Jeromy Burnitz led off the fourth with singles and Bay scored on Castillo's fly to right, cutting Houston's lead to 2-1.
Maholm retired nine of the next 11 Astros he faced after Biggio's homer.
"The first inning was rough. I just wasn't throwing very well," Maholm said. "But I made the adjustments because I knew if I didn't, it would be an early night. I had to keep battling."
Houston rallied for another run in the sixth.
With one out, Morgan Ensberg walked for the second time and Wilson followed with a single to left. Ensberg went to third on Chris Burke's flyout and scored on Everett's double into the left-field corner. Everett has six RBI in his last seven starts.
"Big run, gave us a little breathing room," Astros manager Phil Garner said. "That really made a big difference in the game."
Backe retired 10 of his last 11 batters. Garner said he looked even sharper than he did in his last start, when he allowed one run and seven hits in a 7-1 win at San Diego.
"He used all his pitches, located very well, stayed down," Garner said. "He did a very good job."
Luke Scott, batting .403 since he was called up from Triple-A Round Rock on July 13, pinch-hit for Backe in the seventh and doubled off Pittsburgh reliever John Grabow.
The Astros won their third straight series opener. They feel as though they have to win virtually every series the rest of the way to have a chance to win the tight race for the NL wild card.
"It's huge," Backe said. "We got this one off our back. We win another one, either tomorrow or the next day, we've won another series. That's what we have to do from here on out."
Biggio's home run total ranks fourth all-time among second basemen. He needs seven homers to tie Ryne Sandberg for third. ... Houston's Willy Taveras had a bunt single in the fifth to extend his hitting streak to 11 games. ... The Astros will call up RHP Jason Hirsh from Triple-A Round Rock to start Saturday against San Diego. The team said it would make a corresponding roster move later this week. ... Pittsburgh dropped to 11-41 when scoring four runs or fewer.