Hunter Pence put the Astros in front with a two-run homer in the first inning and Brett Wallace completed a four-run initial frame with a two-run single for the Astros.
The win enabled Houston to salvage a split in their four-game series with the Dodgers.
Gustavo Chacin (2-2) earned the victory after getting starter Nelson Figueroa out of a jam in the top of the fifth.
Ramon Troncoso (1-3) was saddled with the loss after allowing the RBI hits by Castro and Blum.
Jay Gibbons smacked a three-run homer for the Dodgers, losers of seven of nine.
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