Trumbo's first-inning shot off Christian Friedrich (4-2) gave the Angels a quick 3-0 lead, while his second long ball broke a 6-6 tie, sending the Angels to their fourth win in five games and ninth straight on the road.
Torii Hunter went 3-for-6 with a two-run homer and three RBI, and scored three runs for Los Angeles.
Ervin Santana (3-7) earned the win despite a shaky outing, allowing seven runs on nine hits over 5 2/3 innings.
Friedrich, meanwhile, was rocked for nine runs (eight earned) on 10 hits over four full frames.
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