Trailing 2-1 entering the eighth, the Angels scored four times to grab the lead.
Mike Trout and Torii Hunter (3-for-4) led off with singles against Mariners starter Felix Hernandez (13-6) and Trout came in to score the tying run when Seattle third baseman mishandled Albert Pujols' grounder.
Hunter went to third and Pujols to second on the error, bringing up Trumbo, who lashed a pitch through the hole for a two-run hit.
Howie Kendrick capped the rally with an RBI double.
Ervin Santana (8-11) won for the third time in four games, yielding a pair of runs on four hits over seven innings.
Kevin Jepsen tossed a scoreless eighth and Ernesto Frieri picked up his 17th save as the Angels clinched their three-game series.
Hernandez finished by allowing five runs (four earned) on nine hits -- just the second time in the last 11 starts that he has allowed more than two runs.
Trayvon Robinson socked a solo homer for the Mariners.