HOUSTON — The Houston Astros are playing better and manager Cecil Cooper says it's due to improved starting pitching.

The Astros also showed some offense Friday night, complementing Mike Hampton's strong outing in a 9-1 victory over the Pittsburgh Pirates.

Carlos Lee hit a grand slam, and Hampton struck out five to beat Pittsburgh for the ninth straight time. Houston has won six of its last eight games and the victory margin in this one was the largest of the season.

"It feels like every game we play out there is a battle," Lee said. "It felt good to just relax out there. It's not like there was a lot of pressure."

Hampton (4-4) allowed five hits in seven innings, holding the Pirates to one run for the second time in a week. The 36-year-old left-hander also pitched seven innings in Houston's 2-1 win at PNC Park last Sunday.

"This is basically the same game he pitched against us the last time," Pirates manager John Russell said. "We just did not have many opportunities."

Hampton, who signed with the Astros as a free agent in December, won at Minute Maid Park for the first time in eight starts since April 2003, when he pitched for Atlanta. He also had a hit and an RBI, increasing his batting average to .381, the best among major league pitchers.

Lee's 13th career grand slam — off Evan Meek — capped a seven-run sixth inning for Houston. Humberto Quintero drove in two runs with his first career triple earlier in the inning off Jeff Karstens (2-3).

The 26-year-old right-hander beat the Astros last Saturday and held them to two runs through five innings before falling apart in the sixth.

"I had a chance to win the game," Karstens said. "I was just trying to keep us in it and then things got away from me."

Lance Berkman led off with a walk and advanced on Geoff Blum's flyout to right. With Edwin Maysonet batting, Berkman bolted for third, his first stolen base of the season.

Maysonet walked before Quintero tripled off the right-field wall, and Quintero came home on Hampton's sacrifice fly to right to make it 5-1.

Michael Bourn doubled before Russell brought in Meek to relieve Karstens. Meek walked Jeff Keppinger and Hunter Pence before Lee drove an 0-1 pitch off the brick facade in left, his 10th homer of the season.

That was more than enough support for Hampton, who improved to 13-3 in 19 career starts against the Pirates, his best record against any team.