OAKLAND, Calif. -- Cliff Pennington's first thought was to bluff tagging up from first base. Instead the Oakland shortstop took advantage of a poor throw back to the infield by Seattle center fielder Franklin Gutierrez and a wild pitch by Brandon League to move into scoring position.
From there, Kurt Suzuki did what the A's have come to expect from their veteran catcher.
"[Pennington] just really made a heads-up play and put us in a position to win," A's manager Bob Geren said. "It's big. We're preaching aggressiveness. If you stay aggressive, good things happen."
Pennington drew a one-out walk from League (3-4), advanced to second on Daric Barton's fly out and took third on a wild pitch. After Ryan Sweeney was intentionally walked, Suzuki hit a 1-1 pitch from League up the middle, just past diving shortstop Matt Tuiasosopo.
Pennington, Oakland's leadoff hitter, also had a double but had struck out in the seventh before coming up big in the 10th.
"It was one of those ones where I was going back to tag and I was going to go about halfway and see where we were at," Pennington said. "I just took off hard and when he made the throw I felt like I could beat it so I kept going."
Ryan Sweeney matched his career high with four hits, Rajai Davis had three hits, including two infield singles, and Jack Cust drove in his first two runs since being called up from the minors as the A's swept the two-game series from Seattle following a season-high five-game losing streak.
Seattle catcher Rob Johnson homered and threw out two baserunners in scoring position but the Mariners bullpen blew a late lead, which kept ace Felix Hernandez winless over his past five starts.
Oakland had a season-high 16 hits overall, one day after matching its previous high of 15.
The teams used five pitchers each and the game featured three ties and three lead changes before Suzuki's eighth career walkoff hit.
"There were a couple of critical mistakes that came back to haunt you and maybe put the game in extra innings as opposed to winning it," Seattle manager Don Wakamatsu said. "Those are things guys have to be accountable for, especially when the play's in front of you."
Oakland reliever Craig Breslow (1-1) pitched one scoreless inning for the victory.
The game began as a pitching duel between Hernandez and Oakland's Ben Sheets, but neither starter was around for the decision.
Hernandez, who received a no-decision when he faced the A's on opening day, fell behind early and would have been in a bigger hole had it not been for Johnson throwing out two baserunners.
Johnson, who has been limited recently due to back stiffness, hit a one-out home run in the third.
Hernandez finished with six strikeouts and allowed a season-high 11 hits but hung around long enough for Seattle to get the lead before the bullpen let it slip away, preventing him from earning his first win since April 21.
Sheets, coming off two solid starts, lasted 6 2/3 innings and gave up eight hits and four runs.
The A's hit four doubles off Hernandez, the most the righty has allowed since Sept. 31, 2008. ... Seattle demoted winless left-hander Ryan Rowland-Smith to the bullpen and replaced him in the rotation with right-hander Ian Snell. The move comes one day after Rowland-Smith gave up a career-worst seven runs in 2 2/3 innings in an 8-4 loss to Oakland. "I think mentally it will be a good opportunity for him to get a little bit of a break," Wakamatsu said. "Ian's been throwing the ball well out of the bullpen and it gives him a chance to get back in there and give Rowland-Smith a break." ... LHP Dallas Braden (4-3) will start for Oakland against Detroit on Wednesday in his first appearance at home since pitching a perfect game against Tampa Bay on May 9. ... Ken Griffey Jr. singled in the eighth to break an 0-for-18 drought. He was replaced by pinch-runner Ryan Langerhans, who scored Seattle's fifth run.