PITTSBURGH — The Houston Astros figured out how to take the pressure off themselves — and that's how they earned the chance to play pressure-packed games during the last week of September.

Craig Biggio drove in three runs and Andy Pettitte pitched the surging Astros to their seventh straight victory Tuesday night, 7-4 over the Pittsburgh Pirates.

Mike Lamb scored three times for second-place Houston, which moved within 1½ games of fading St. Louis in the NL Central. The Cardinals lost their seventh straight, 7-5 to San Diego.

A week ago, the NL champion Astros seemed just about done. All of a sudden, they're right in the middle of another pennant race.

"This is unbelievable right now," Pettitte said. "I mean, really, you don't know what to say. ... Maybe we ought to keep saying we got no shot, you know?"

Pettitte won his third straight decision and the Astros improved to 79-78, the first time they've been over .500 since June 22 — the day Roger Clemens made his initial start of the season in a loss to Minnesota.

"This game's supposed to be fun," said Houston's Luke Scott, who had two hits, two runs and an RBI. "You're supposed to go out there and play the game and not try to force results to happen. You run into trouble a lot of times when you do that. You've just got to take what they give you and just play hard every day and not worry about the results."

The Astros gathered in the clubhouse after their game to watch the Padres rally past the Cardinals.

"We're playing good ball now," manager Phil Garner said. "We're doing the kind of things that I like to see our team do. We're coming up with some big hits when we need them."

Jason Bay and Jose Bautista homered for the Pirates, who have lost five in a row but had won eight of nine at home. Pittsburgh's Freddy Sanchez went 4-for-5 to raise his NL-leading batting average to .346.

Sanchez now leads by 11 points over Florida's Miguel Cabrera, who went 1-for-4 in a loss to Cincinnati.

"I don't think it's over yet," Sanchez said. "I just have got to take it one game at time."

Houston jumped on Ian Snell (14-11) for three runs in the first inning. Scott's single scored Lamb, who walked with one out. Aubrey Huff singled home Lance Berkman two batters later, and Biggio followed with a groundout that scored Scott.

After Pettitte retired the Pirates in order in the first, Bay led off the second with his 35th homer — a shot to right on a 2-0 pitch.

Three batters later, Bautista hit a two-run homer, his 16th, to tie the score at 3.

But that was all the Pirates could manage against Pettitte (14-13), who scattered 10 hits and a walk while striking out two. He improved to 7-1 lifetime against Pittsburgh.