OAKLAND -- The A's turned on the power switch in the eighth inning on Sunday to move closer to their first postseason appearance since 2006.
Yoenis Cespedes connected on his 23rd home run to break a 2-2 tie and Josh Reddick added a tape-measure blast to send the A's to a 5-2 win and series sweep of the Mariners on Sunday.
Oakland recorded its fifth win in six games and 15th in 20 outings at home.
Cespedes sent a two-strike delivery from Mariners reliever Shawn Kelley (2-4) several rows into the bleachers down the line in left. Cespedes stood at home plate waiting to see whether the ball would stay fair before breaking into his home-run trot.
Reddick deposited his 32nd homer in the second deck in right also just inside the foul pole. His blast came off of Mariners reliever Lucas Luetge, who had surrendered a single one batter earlier to Brandon Moss.
The A's have hit 20 homers in the last nine games and have a Major League-leading 110 since the All-Star break.
Grant Balfour recorded his 22nd save in 24 opportunities to make a winner of A's reliever Sean Doolittle (2-1).
The A's jumped on top with two runs in the first inning.
Stephen Drew walked and scored from first on a Cespedes triple that looped down the right-field line with the Mariners playing the right-handed hitter to pull. Moss' fly to medium-deep center plated Cespedes.
The Mariners tied the game in the third with two of their own. Seattle leadoff batter Franklin Gutierrez laced his second two-strike double in as many at-bats. Casper Wells beat out an infield single to third base and Kyle Seager's single through the hole at short scored Gutierrez.
A's starter Tommy Milone, who labored with 67 pitches through three innings, induced a ground-ball double play from Jesus Montero, but surrendered a game-tying RBI single to Justin Smoak with two outs.
An outstanding throw to the plate by A's right fielder Reddick helped Milone out of a second-inning jam. Carlos Triunfel's one-out single was initially bobbled by Reddick, who recovered to throw a strike to catcher George Kottaras to cut down Smoak trying to score from second.
Mariners starter Erasmo Ramirez settled down nicely, not allowing a hit after a Cespedes' two-out infield single in the third until designated hitter Seth Smith singled to center with one out in the sixth. Ramirez gave way to the bullpen having allowed only three hits.
A's reliever Ryan Cook surrendered a double and single to start the seventh, but reached back to strand the runners at first and third by striking out Wells, Seager and Montero. Both Wells and Seager offered at 2-2 fastballs while Montero watched a curve slice the middle of the plate on a 1-2 count.
NOTES -- Oakland manager Bob Melvin said Brett Anderson may throw a bullpen session on Monday as the injured starter still has an eye on returning before the end of the playoffs. Seattle's Gutierrez left in the third inning with tightness in his left groin. ... The A's on Monday play the first of three final regular-season games. The pitching matchups against visiting Texas include Jarrod Parker (12-8) vs. Martin Perez (1-3) on Monday, Travis Blackley (5-4) vs. Matt Harrison (18-10) on Tuesday and A.J. Griffin (7-1) vs. Ryan Dempster (7-3) on Wednesday. ... The Mariners finish the season with three games against the visiting Angels in a series that starts on Monday with Felix Hernandez (13-8) set to oppose C.J. Wilson (12-10).