Moore hit his fourth home run of the season in the third inning and Ichiro Suzuki had two hits to get within 19 of his 10th consecutive 200-hit season.
Doug Fister (5-11) went five innings for the win. Fister threw 93 pitches over five innings, giving up two runs on five hits.
Fister was helped out by a five-run Seattle second inning that put the Mariners on the road to snapping a six-game losing streak in Oakland.
Dallas Braden (9-11) took the loss with six runs on nine hits over five innings.
The A's trailed by five runs going into the ninth but rallied for three runs, two on a single by Coco Crisp, and had the winning run at the plate. Closer David Aardsma, however, came in and retired Cliff Pennington on a soft fly out to left field for his 29th save.
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