The score was tied 3-3 in the seventh when the Astros put L.J. Hoes and Carlos Corporan aboard with two outs and Dominguez followed by hammering the first pitch he saw from Juan Gutierrez (0-4) into the Astros' bullpen for a three-run shot.
Dominguez finished 4-for-5 while Hoes added three hits, including his first major-league homer, as the Astros took 2-of-3 from the Angels.
Brett Oberholtzer (3-1) went six innings to earn the win, allowing three runs on seven hits. The rookie left-hander walked one and struck out four.
Kevin Chapman recorded the final two outs to collect his first big-league save for Houston.