Berkman had an RBI double and scored three runs for the Astros, who have won four straight and 12 of 13. Houston's 34-16 record is the best in the majors since the All-Star break and the Astros are emerging as a factor in the NL wild-card race.

Houston came into Tuesday's game trailing Milwaukee by five games, Philadelphia by two and St. Louis by a half-game.

After the victory, the big-screen television in the Houston clubhouse was tuned to the Cubs-Cardinals game, in time to see St. Louis win in the ninth inning. Someone quickly changed the channel to the Reds-Brewers game that was in extra innings.

"We're going to try to win as many games as we can," Berkman said, "and we're certainly going to pay attention to what the teams in front of us are doing."

The Astros have made a habit of finishing strong. In 2004, they went 48-26 in the second half to make the playoffs. In 2005, they went 45-30 after the break and reached their first World Series.

Berkman acknowledged that Houston needs a "miracle" to make the postseason this year, but no one in the clubhouse is giving up hope.

"The main issue is trying to win each game and if for some reason, there is a spot for us, that'd be great," Wolf said. "But it's just fun winning, just keep going out there and playing good baseball."

Wolf (10-11) allowed four hits and struck out four in seven innings to improve to 4-1 in nine starts since the Astros acquired him from San Diego on July 22. The Astros have won eight of the nine games Wolf has started for them.

Hunter Pence hit a ball that bounced off the top of the wall in right field for an RBI double in the sixth that prompted the second use ever of instant replay. Umpires looked at the replay and ruled that it was not a home run, upholding the original call.

Baseball started allowing umpires to use instant replay to determine boundary calls on Aug. 28. Last Wednesday, a home run by Alex Rodriguez was reviewed and upheld in the New York Yankees' 8-4 win over Tampa Bay.

The rest of Tuesday's game in Houston was clear cut.

Houston led 6-2 after four innings against Ross Ohlendorf (0-1), who was making his second career start. The Pirates have lost four straight and 15 of 18.

The Pirates scored two runs in the first, after Wolf walked leadoff man Nate McLouth. Freddy Sanchez grounded out before Ryan Doumit lined an RBI single to left. Adam LaRoche then doubled down the right-field line, scoring Doumit.

Darin Erstad and Miguel Tejada singled in the bottom of the first before Berkman drove a 2-1 pitch into the left-field porch for his 28th homer.

Erstad and Tejada both singled again in the third and this time, Berkman doubled to score Erstad and make it 4-2. The Astros loaded the bases and tacked on another run later in the inning.

"I didn't feel like I consistently made pitches I needed to," Ohlendorf said. "I got into bad counts and put the ball over the middle of the plate. I need to locate my pitches better."

Michael Bourn singled with two outs in the Houston fourth, stole second and went to third on Ohlendorf's balk. Erstad drove in Bourn with a double to left center.

"Offensively, we did a nice job and Wolf gave us another quality start," Berkman said. "The bottom line, we swung the bats well tonight."

Wolf retired 13 consecutive batters after LaRoche's double. Pinch-hitter Robinzon Diaz broke Wolf's streak with a two-out single in the fifth, but McLouth popped out.

"The start was a little rocky, but I kind of settled down as the game went on," Wolf said.

Berkman led off the Astros' fifth with a single off reliever Jason Davis and scored again on Geoff Blum's triple to the right-field corner. David Newhan added an RBI single in the inning to make it 8-2.

Steve Pearce hit his first career homer for the Pirates in the seventh, Pittsburgh's first home run in 43 innings.

Notes

Sanchez left in the second inning with blurred vision in his right eye and was replaced by Luis Rivas. ... Berkman has scored 891 runs in his career, moving past Cesar Cedeno and into third place in franchise history. Berkman has 109 runs this season, one shy of a career high. ... Houston manager Cecil Cooper said LHP Wandy Rodriguez will miss his next scheduled start after straining his right oblique muscle Sunday against Colorado.