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MIAMI -- The Houston Astros are running out of time to solve their problems at the plate.

Jorge Cantu hit a three-run homer and rookie Chris Volstad allowed one run in eight innings to lead the Florida Marlins to a 5-1 win over the Astros on Tuesday night.

The Astros, who have lost three straight, entered the game 2 1/2 games behind Milwaukee and Philadelphia in the NL wild-card race.

"We've got to figure out a way to get our offense going a little bit," Astros manager Cecil Cooper said. "Either they're making good pitches or we're not making good swings. Something's not happening."

Cantu's three-run homer in the first inning stopped Houston ace Roy Oswalt's franchise-record scoreless innings streak at 32 1/3 innings. Oswalt (15-10), who had lasted at least eight innings in five of his previous six starts, allowed five runs -- three earned -- and six hits over six innings. He struck out 10 to tie his season high.

"We're playing the same way we did a month ago. We're just trying to go out there and play nine innings and see if we can win," Oswalt said. "Tonight, we got behind early and never caught up."

Volstad (5-3) gave up four hits in his first start against the Astros and the second-longest outing of his career. The rookie right-hander struck out four and didn't walk a batter.

"After the game someone told me 97 pitches, 72 fastballs," Volstad said. "I just mixed in some off-speed pitches to keep them off balance but it was mostly the two-seamer."

Florida's lineup rattled Oswalt early. After Cantu's home run -- his 27th of the season -- Dan Uggla scored on a double by Cody Ross to give the Marlins a 4-0 lead. Oswalt then hit Alfredo Amezaga with a pitch, which drew warnings for both teams.

In the second inning, Mike Jacobs doubled to the deepest part of Dolphin Stadium to score Hanley Ramirez and make it 5-0. Oswalt settled down after Jacobs' double, but the damage was done.

"When you make mistakes, they make you pay," Cooper said. "These guys are one of the better hitting clubs as far as hitting home runs, and in this ballpark if you make a mistake and you get it out over the plate, they usually hurt you."

Michael Bourn doubled to open the eighth inning and advanced on Brad Ausmus' fly to right. He scored on pinch-hitter Kazuo Matsui's groundout to make it 5-1.

Ramirez, who scored two runs for Florida, doubled in the seventh inning and Amezaga hit his second triple in two games in the eighth.

"It's just baseball, it's crazy sometimes," Cantu said. "If you play hard you're going to get results."

The Astros had won 14 of 15 before Hurricane Ike convinced Major League Baseball to move two home games against the NL-leading Chicago Cubs to Milwaukee, where Houston struggled.

"We're just not getting the job done," Ausmus said. "We haven't done anything offensively. We're barely scraping out a run."

Houston got no-hit by Carlos Zambrano to lose the opener 5-0, then was held to one hit in a 6-1 defeat Monday. In 53 at-bats (59 plate appearances) on Sunday and Monday, the Astros had managed one hit and four walks.

"We haven't hit well the last several games and a lot of that is who we've been facing," Lance Berkman said. "[Volstad] has a deceptive fastball, a lot of late movement on it. This is a good team. They were in contention until just a little bit ago."

The Marlins, winners of their last six, seem to think they still are. When the final out was recorded in New York's 1-0 loss to Washington, a cheer went out in Florida's clubhouse.

"That's the beauty of the pennant race, everybody is just thrilled to be in this," Cantu said. "We're not out, we're not out. Until we have that little 'x' next to our team name, that's when everything's over. But since we don't have that 'x' next to the team name, we're still in this thing."

Game notes

RHP Brandon Backe, a native of Galveston, Texas, is scheduled to start Wednesday. Galveston was torn apart when Hurricane Ike made landfall Saturday as a Category 2 storm. ... C Paul Hoover was designated for assignment to make room for INF Gaby Sanchez on Florida's roster.