Halladay (2-0) scattered seven hits and retired the last nine Astros in order. Acquired from Toronto in an offseason trade, the former AL Cy Young winner pitched his 50th career complete game and outdueled Roy Oswalt (0-2).
Houston dropped to 0-6. The two-time NL champion Phillies improved to 5-1.
Oswalt also struck out eight and allowed five hits in six innings, but lost for the first time in his last seven decisions against Philadelphia.
Jimmy Rollins led off the game with a home run. Philadelphia mustered only six hits, its first game under 10 hits this season.
