Miller knocked a solo shot in the third inning for a 3-1 Seattle lead, then connected with Dustin Ackley, Mike Zunino and Nick Franklin aboard in the fifth to break the contest open.
Justin Smoak added a two-run shot for the Mariners, who evened their season-ending three-game series against the American League West champion Athletics.
Brandon Maurer (5-8) allowed two runs on six hits over 5 1/3 innings to collect the win and Danny Farquhar finished up with his 16th save.
A's starter Jarrod Parker (12-8) had a rough tuneup for the post-season, surrendering seven runs on seven hits over just 4 1/3 innings.
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