HOUSTON (Ticker) -- Mike Lamb had waited for a couple of days for his first at-bat of the season. When he finally got it, he made it count.

Lamb came off the bench to deliver a two-run triple in a three-run, eighth-inning rally as the Houston Astros posted a 4-1 triumph over the St. Louis Cardinals.

Hitting for Brad Ausmus with two aboard and one out, Lamb fouled off four pitches by Julian Tavarez before driving the ball to center field, scoring Morgan Ensberg and Jason Lane to break a 1-1 contest.

"I was kind of hoping that my first at-bat would not be with runners on and late in the game with a chance to win or lose," Lamb said. "But it's my job and I have to be ready at any time in the game. I enjoy giving my team a chance to win."

Lamb said he thrives on the pressure that comes with pinch-hitting and hitting the ball in the gap was the secret to his success today.

"I don't want that to go nationwide," Lamb joked. "There's an old saying and the grammar is improper. But you have to hit it where they ain't. That usually works out for the best."

The Astros, who had 15 hits, tacked on another run when Willy Taveras singled to center, scoring Lamb for a three-run edge.

Chad Qualls (1-0) pitched the seventh and eighth innings and retired all six batters, needing just 14 pitches in his first outing of the season.

After walking David Eckstein to lead off the ninth, Brad Lidge retired Larry Walker , Albert Pujols and Scott Rolen on 11 pitches to record the save.

"We got a little bit from everybody today," Astros manager Phil Garner said. "(Lamb) really picked up right where he left off last year. He comes through for us when we really needed him. He had a really good at-bat against Tavarez and put a good swing on that pitch."

Making his first start since season-ending elbow surgery last August, Andy Pettitte threw just 71 pitches in six innings, allowing one run and four hits. He did not walk a batter and struck out three, surrendering a homer to Reggie Sanders in the fifth.

"I never imagined that I would be able to go out there and give them six innings with the pitch count where it was," Pettitte said. "It was great to go back out there and not have to pitch with a lot of pain."

"He did his best," Ausmus said. "He moved his fastball in and out. He jammed their righthanded hitters and he used all his pitches. He just kept the ball off the barrel of their bats. He did a nice job and that was a great first outing for him. "

Tavarez (0-1) allowed four hits and three runs in the eighth.

Houston opened the scoring in the third, when Jeff Bagwell drove a 3-2 pitch to center for his first hit of the season, scoring Craig Biggio .

The Cardinals were held to just four hits and Eckstein's single in the sixth was their only one over the final four innings.

"Overall, they just pitched well," Cardinals manager Tony La Russa said. "Pettitte just moved the ball around when he had to. He may not have had all of his weapons, but (Greg) Maddux won 300 games doing that."

Sanders homered for the second straight contest.

"I just took what they gave me today," Sanders said. "(Pettitte's) velocity is not what it has been in the past. But we didn't know what to expect because he has been out so long."