J.J. Putz (1-4), who had set the Diamondbacks down 1-2-3 in the ninth, walked Justin Smoak and then gave up a single to Dustin Ackley to lead off the 10th. Brad Ziegler came on and Brendan Ryan moved the runners up with a sacrifice bunt before Wells came through with the game-winning single to right.
Ichiro Suzuki had four hits, including an RBI double in the 10th that accounted for the final score.
Charlie Furbush (3-1) pitched two scoreless innings in relief to get the win for the Mariners, who won for the third time in their last four games.
Tom Wilhelmsen was perfect in the bottom of the 10th for Seattle, picking up his fifth save.