The A's moved 5 1/2 games ahead of Seattle for the final AL wild-card slot.
Edwin Jackson (5-3) allowed one run on three hits in six innings. He improved to 5-0 with a 1.30 ERA in five career starts against the Mariners.
Seattle starter Felix Hernandez (8-13) is 0-7 over nine outings since beating the Royals on June 30.
A day after the Mariners held on for an 8-7 win, they took a 1-0 lead into the fifth. Piscotty tied it with a home run added a sacrifice fly in a four-run sixth.
Piscotty hit his 21st homer, a three-run drive, in the eighth. He has three career multihomer performances and matched his big league high for RBI in a game.
Hernandez retired the first seven hitters in order before Chad Pinder's one-out single in the third. The right-hander then got two consecutive inning-ending double plays to face the minimum through four.
Hernandez allowed four runs and four hits in five-plus innings, struck out three and walked two. He has made a minor mechanical change and had been commanding his fastball better, though he threw two wild pitches in the costly sixth.
The A's bounced back a day after striking out 18 times. Manager Bob Melvin used an Oakland-record 24 players for a nine-inning game and nine pitchers -- a franchise high for nine innings.
Seattle leadoff man Mitch Haniger opened the game with a double for a career-best 14-game hitting streak. Khris Davis, who hit his majors-leading 40th homer Saturday night for the A's, went 0 for 4 with two strikeouts.
This lopsided result wasn't a common occurrence when these teams play each other. Of their 16 matchups this season, eight have been decided by one run and three more by two runs. They have one series remaining, at Safeco Field from Sept. 24-26 during Oakland's final road trip.
Mariners: LHP Marco Gonzales, on the disabled list retroactive to Aug. 24 with a strained neck muscle, was tentatively scheduled to pitch off a mound Monday in a light bullpen session. "I'm much more encouraged based on what the trainers have told me the last couple days," manager Scott Servais said.
Athletics: RHP Andrew Triggs (nerve irritation in his pitching arm) threw a 30-pitch, two-inning simulated game Saturday and said he "felt great." While Melvin said Triggs would be re-evaluated to determine his next step, the pitcher expects to have a rehab outing Wednesday at Class A Stockton. ... LHP Brett Anderson (strained pitching forearm) threw on flat ground Sunday and could work off a mound as soon as Monday.
LHP CC Sabathia (7-5, 3.36 ERA) pitches back home in the Bay Area looking for just his second victory in eight starts when the New York Yankees -- who hold the top AL wild-card spot -- visit for a three-game series that begins with an afternoon contest on Labor Day. RHP Trevor Cahill (5-3, 3.60), 4-0 with a 0.85 ERA in eight home starts, pitches for the A's needing four strikeouts to reach 1,000 for his career.
Seattle returns home to host Baltimore, with RHP Erasmo Ramirez (1-3, 6.28) pitching Monday's series opener.