HOUSTON -- Brad Hennessey impressed San Francisco catcher Mike Matheny with his poise after giving up home runs to two of the first three hitters Thursday night.
"His composure is definitely something to be complimented," Matheny said. "It shows he's a gutsy pitcher. He has shown that a couple of times this year.
"He doesn't let situations bother him. A young guy usually starts second-guessing himself in those spots, but he doesn't."
Hennessey (2-0), recalled from Triple-A Fresno earlier in the day to make his second start of the year and ninth of his major league career, overcame the rough start to help the Giants beat the Houston Astros 6-3. The right-hander allowed three runs on six hits in six innings, struck out seven and walked three.
"You can't let (the home runs) bother you," Hennessey said. "Otherwise, you'll self-destruct. After those two pitches, I concentrated more and trusted my sinker.
"It's great that my teammates and manager had confidence in me tonight. It helps me build confidence in myself."
Manager Felipe Alou also praised Hennessey.
"I like Hennessey," Alou said. "I liked him last year but we didn't have room to give him a good shot in spring training. He did the same thing in Pittsburgh this year, giving up a couple of runs early then settling down. Tonight after the first inning, he dominated."
Matheny singled in the tying run in the sixth inning and Houston outfielder Lance Berkman's error on the play allowed the go-ahead run to score.
With the Giants trailing 3-2 in the sixth inning, Matheny, who was 2-for-4 with two RBI, hit a bases-loaded single to left that Berkman misplayed for an error, allowing Edgardo Alfonzo to score to make it 4-3.
Tyler Walker pitched the ninth for his second save in three chances.
Craig Biggio hit two home runs, and Morgan Ensberg also connected for the Astros.
The Astros have lost three straight and nine of 10 to fall to 12-22, 10 games behind first-place St. Louis in the NL Central.
They held a 30-minute team meeting after the game.
"We had a team meeting tonight because we needed it," manager Phil Garner said. "I said a few things and several players said some things and it was good.
"The only reason you call meetings is because you aren't winning. There's no question that everyone is trying too much. What encouraged me tonight is that we got more guys on base and we had several opportunities and I think things will start happening soon."
Ensberg had two of Houston's season-high four errors.
"I had a bad defensive game during a bad time to have it," Ensberg said. "The errors are a sign of trying to do too much and those are the things I just have to adjust. I was trying to do Part I without Part II."
Houston's Andy Pettitte (2-4) allowed four runs, two of them unearned, on five hits in six innings. Pettitte, who struck out six and walked three, retired 11 in a row from the second to the fifth inning.
"We're going through some tough times and we just have to keep pushing and grinding," Pettitte said. "Nobody in this league is going to feel sorry for us, especially as successful as this club has been the last several years. We have to find a way to turn it around."
The Giants scored an unearned run in the first inning when Jason Ellison singled and moved to second on Ensberg's error at third base. After a fielder's choice, Ellison scored on Moises Alou's sacrifice fly.
Biggio homered leading off the bottom of the first, his fourth home run of the year, and Ensberg followed with his third homer to give the Astros a 2-1 lead.
Biggio has a National League-record 42 career homers leading off a game. He's third in major league history behind Rickey Henderson (80) and Brady Anderson (44).
The Giants tied it in second on Matheny's RBI single, and Biggio hit his second home run with one out in the fifth to make it 3-2.
San Francisco added two insurance runs in the eighth on Omar Vizquel's RBI single on Ensberg's error on Alou's grounder.
Biggio has 14 career two-homer games. ... Houston's Willy Taveras moved back into the NL lead in stolen bases with his 11th and 12th, both in the third inning. ... Houston's Jason Lane singled in the sixth inning to snap an 0-for-17 streak. ... The Giants are 16-3 at Minute Maid Park. They won their first 11 games in the ballpark.