OAKLAND -- The A's turned the power switch on 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.
In recording its fifth win in six games and 15th in 20 outings at home, Oakland moved to within two games of A.L. West-leading Texas, which split a doubleheader with the Los Angeles Angels Sunday. The A's reduced their magic number for clinching at least a wild-card berth to one against both the Angels and the Tampa Bay Rays.
The A's would need to sweep Texas in its three-game series against the Rangers to claim the division title.
"We feel like we can win every game, that's how we're playing right now," said A's starter Tommy Milone.
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.
"We feel pretty good going into the late innings of a close game," A's third baseman Josh Donaldson said before singling out Cespedes and Reddick for coming through late. "That's awesome, that's what these guys have been doing all year."
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 Mariners, meanwhile, lost for the sixth time in seven games and finished September going only 9-17 after having winning months in July (15-11) and August (15-12). Seattle stranded eight runners on Sunday as the team's inability to deliver key hits with runners on base continues to haunt the Mariners.
"It's really been the story of our season offensively," Seattle manager Eric Wedge said. "Eleven hits but only two runs, we've got to do better than that."
A prime example of Seattle's inability to capitalize occurred in the seventh when A's reliever Ryan Cook surrendered a double and single to start the frame, but struck out the side to leave runners stranded at first and third in a 2-2 game.
"There's a time you have to put the ball in play -- shorten up and just make contact," Wedge said.
The A's scored twice in the first as Cespedes tripled in Stephen Drew and scored on a sacrifice fly to center off of the bat of Brandon Moss.
The Mariners tied it in the third. 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.
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. Reddick has 15 outfield assists this season.
"Huge, but he's been doing it all year so it's not surprising," Milone said of Reddick. "It's a good feeling when you've got guys out there who have been doing it all year long."
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 Mariners streak of 18 consecutive games with at least one home run was snapped. ... 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 series that starts on Monday with Felix Hernandez (13-8) set to oppose C.J. Wilson (12-10).