Volstad (5-3) allowed one run on four hits and struck out four batters for the Marlins, who have won six straight and trail the New York Mets by five games in the National League East. New York lost to Washington 1-0 Tuesday.

Jorge Cantu hit a three-run homer and Hanley Ramirez scored two runs for the Marlins.

Michael Bourn scored the lone run for Houston, which came into Tuesday's action 2 1/2 games back in the race for the NL wild card.

Astros starting pitcher Roy Oswalt (15-10) entered the game with an 8-1 mark in his last 10 starts but allowed five runs on six hits over six innings with 10 strikeouts.