Grant Green's bases-clearing double in the second inning staked the Angels to a 3-0 lead and Cowgill's solo shot in the third made it 5-1 Los Angeles.
The Angels got a decisive sixth run in the seventh when Cowgill tripled with none out and broke for home with Andrew Romine at the plate. Mariners hurler Joe Saunders uncorked a wild pitch on the play, and Cowgill scored without a play.
Jerome Williams (9-10) earned the decision, allowing one run on five hits over 5 2/3 innings as the Angels notched a sixth victory in seven games.
Saunders (11-16) ended up yielding six runs on six hits over seven innings for Seattle.
Raul Ibanez bashed his 300th career homer and 29th of the year for the Mariners.
Notable deaths of 2014 [PHOTOS]