HOUSTON -- Roy Oswalt is still thinking about the one that got away.
Oswalt, who has won 20 games in each of the last two seasons, improved to 4-0 for the first time in his career but afterward remembered his no-decision in his second start this season -- Houston's 12-8 loss to Washington.
"All I can think of is that I wish I was 5-0," Oswalt said. "I got that no decision and I keep thinking about (how) I should have been able to keep that lead."
Oswalt allowed six hits and one run against the Pirates in his 150th career start. He's on a seven-game winning streak and hasn't lost since September.
"Roy set a really good pace for the game," Astros manager Phil Garner said. "He was in a good rhythm."
The Astros jumped on Pirates starter Paul Maholm early, tagging him for four runs and five hits in the first inning.
Ensberg extended his hitting streak to a career-high 10 games with a two-run homer to center field in the first. He has homered in seven of the last eight games. He also became the first third baseman in franchise history to hit nine home runs in April.
"I think it helped that our offense was aggressive from the start and our pitching has just slammed the door in their faces when we've gotten ahead in this series," Garner said.
Biggio homered for the second day in a row, this one to left field on Maholm's pitch. It was his 46th career leadoff homer, which is second behind Rickey Henderson's 80.
"He's a first-pitch swinger and I wanted to throw it off the plate and I threw it right down the middle," Maholm said of Biggio's homer. "Right then I knew the ball wasn't going to go where I wanted it to today."
Oswalt, who struck out seven, didn't allow a run until Jack Wilson's two-out single scored Jose Castillo in the fifth inning. Jason Lane's throw home beat Freddy Sanchez, who was tagged by catcher Brad Ausmus.
The Astros got a boost from Chris Burke, who was in the lineup in place of slumping Preston Wilson. Burke had three doubles and an RBI. But despite his strong outing, Garner said Wilson will return to the lineup on Monday.
"I don't think he's much changed from last year," Garner said of Burke. "He's a very confident player. I just think he's more determined now because he wants more playing time."
Wilson was signed in the offseason to bolster Houston's offense but is 0-for-12 in his last three games.
Maholm (0-3) got into trouble again in the third inning when Ensberg scored on Adam Everett's bases-loaded walk after Maholm walked three of five batters he faced in one stretch.
He allowed seven hits and five runs and walked four in three innings.
"Pretty much the whole time I didn't execute any pitches," Maholm said. "Then they hit them hard ... and that's all that happened today."
Pirates manager Jim Tracy said getting behind by so many runs early in the game made a comeback virtually an insurmountable task.
"When you're facing an opponent like the caliber of Roy Oswalt, the last thing you want to do is give him a five-run cushion to work with," Tracy said. "Taking him on is difficult as it is but ... to have a game where you have the opportunity to beat him means that you have to stay somewhat close to him."
Biggio went 4-for-4 to record his fifth game with three or more hits in the last six games. He hit his 612th career double in the fourth inning and scored on a sacrifice fly by Lance Berkman.
Sanchez hit a solo shot off Houston reliever Mike Gallo in the eighth inning.
Houston has won seven of eight while the Pirates have lost four in a row.
- Chad Hedrick, who won a gold medal in speedskating at the Olympics in Turin, threw out the first pitch.
- The Pirates have lost six straight games against Houston since a 7-0 win in September.
- Biggio is now tied with Cap Anson for 21st on baseball's career list for runs scored with 1,712.