In complete control throughout, Webb walked one batter and struck out 10.
Chris B. Young hit two solo homers and had three hits for the Diamondbacks. Chad Tracy had three hits and one RBI for Arizona, which has won four of its last five games.
Hunter Pence drove in Houston's lone run with an RBI groundout in the bottom of the ninth. Carlos Lee had a run and three hits for the Astros, who have split their last four games.
Houston Manager Phil Garner was ejected in the bottom of the seventh for arguing balls and strikes by home plate umpire Dale Scott.
Loser Chris Samson (3-3) gave up three earned runs and eight hits in seven innings with four walks and two strikeouts.