Athletics 4, Mariners 2: Jonny Gomes belted a three-run homer and Tommy Milone tossed six solid innings as visiting Oakland completed a three-game sweep.
Josh Donaldson also went deep for the Athletics, who climbed within 3 1/2 games of first-place Texas in the American League West while maintaining their lead in the wild-card standings.
Oakland, which has won 12 of its last 15 contests, opened the scoring with a two-out rally in the fifth inning. Adam Rosales and Coco Crisp singled before Gomes crushed a 1-1 offering from Jason Vargas, hitting the facade of the upper deck in left field for his 16th blast and a 3-0 lead.
That was enough support for Milone (12-10), who limited Seattle to two runs and eight hits while matching his career high of 10 strikeouts. The left-hander did not issue a walk, and has won three of his last four starts.
Three relievers bridged the gap to Grant Balfour, who worked around a leadoff double in the ninth for his 16th save in 18 opportunities.
Seattle got on the board in the fifth on Michael Saunders' RBI triple. Kyle Seager cut the deficit to 3-2 with a leadoff homer in the sixth, but Donaldson opened the ninth with a shot of his own to create some breathing room.
Vargas (14-10) yielded three runs on four hits over seven innings, walking three and striking out six while falling to 2-1 in five starts against Oakland this year.
Miguel Olivo recorded two hits and stole a base for the Mariners, who have lost six of nine. Seattle has totaled 18 runs in those nine games, scoring more than twice on just two occasions.
GAME NOTEBOOK: Oakland C George Kottaras, who was not in the lineup against the left-handed Vargas, has four home runs and 13 RBIs over his last five games. ... Mariners 3B Alex Liddi went 1-for-3 and scored a run in his first start since June 9. The Italian-born Liddi, who struck out as a pinch hitter Friday, was sent to Triple-A Tacoma on June 12 and recalled Tuesday.