Morgan Ensberg had the kind of power display Jeff Bagwell is no longer capable of because of injury.

An arthritic shoulder is too painful for Bagwell to play, and the Houston Astros announced Sunday night that their slugging first baseman would have surgery next month in hopes of prolonging his career.

Then, Ensberg made sure it wasn't all bad news for the Astros. He hit three home runs to support Brandon Backe's first major league shutout in a 9-0 victory over the San Francisco Giants.

"This certainly was my best game in the big leagues. I was getting the right pitches, seeing the ball well and getting the right swing," said Ensberg, who went 4-for-4 with five RBIs. "It was really a fun game."

Bagwell is the Astros' career leader with 449 home runs, and he had a pair of two-homer games in 1999. But a degenerative shoulder condition has robbed Bagwell of most of his power, and he has only three home runs this season.

Still, Houston knows it will be difficult to replace him in a lineup that has an NL-worst .245 batting average. Bagwell's rehabilitation is expected to last three months.

"A lot of people think that because he can't throw, he can't hit," Ensberg said. "But that's really not the case. Jeff has been getting on base a lot for us and he's still intimidating in the lineup."

Ensberg hit a three-run homer in the first inning off Jeff Fassero (0-1), a solo homer off Jeremy Accardo in the fifth, and another solo shot in the seventh off Jason Christiansen in the 11th three-homer game by an Astros player.

"He was definitely locked in tonight. He didn't miss anything," Fassero said. "The scouting report said to try to throw strikes on the outer part of the plate against him, but he just went the other way with them."

Ensberg overshadowed the best start of Backe's career. Backe (3-2) didn't allow an extra-base hit while throwing 114 pitches in the first shutout by a Houston pitcher since Roy Oswalt against Montreal last Aug. 6. He finished with a four-hitter.

"Early on, I didn't feel that great, but as the game went on I started to realize that something really good could happen," Backe said. "It was the best game I've had and it was nice to get that shutout under my belt.