Justin Maxwell's two-run double earlier in the frame against Anthony Bastardo (2-5) had erased a 4-3 Astros deficit and Domingurez then put the contest away with his key hit.
The rally made a winner of Wesley Wright (2-2), who tossed a scoreless top of the seventh.
Domonic Brown got two back for the Phillies with an eighth-inning double, but Houston's Wilton Lopez earned his sixth save when he retired Carlos Ruiz on a game-ending groundout with two men aboard.
The win gave Houston three victories in its four-game set against Philadelphia.
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