Milone (12-10) worked around eight hits and didn't issue a walk as the A's won for the 12th time in 15 contests overall.
Jonny Gomes unleashed a three-run homer and Josh Donaldson contributed a solo shot for the American League wild card-leading Athletics.
Seattle starter Jason Vargas (14-10) was saddled with the loss, surrendering three runs on four hits over seven frames.
Kyle Seager clubbed a solo homer for the Mariners.
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