Rookie catcher Kurt Suzuki delivered the first grand slam of his career, a second-inning shot into the left field bullpen, and Dan Johnson added one in the ninth to back another strong pitching performance from Joe Blanton.
The two slams and Blanton's seven strong innings helped the A's end a three-game slide with a 9-3 win over Seattle in front of 26,698 fans.
"It's always a good feeling when you barrel a ball up like that," Suzuki said of his grand slam. "I felt good up there, confident. I wasn't trying to do too much, just hit a line drive into the gap."
It's the second time in franchise history Oakland has hit two grand slams in one game.
One, however, proved to be enough for Blanton, who has won five of his last six decisions.
"I just tried to attack the zone," said Blanton (13-9), who allowed two runs on eight hits and a walk over seven innings of work. "Suzuki came up with the big knock, gave me a nice five-run lead and allowed me to go out and attack the zone, throw my game and get a lot of balls in play."
Alan Embree worked two outs into the eighth before giving way to Huston Street, who went on to collect his 13th save in 17 opportunities.
While the win helped Oakland (70-75) end a slide, it continued one for Seattle (75-67). The Mariners have dropped 14 of their last 16 games.
The A's wasted little time feasting on Seattle left-hander
The A's sent nine batters to the plate in the five-run second inning.
Suzuki capped the rally with a grand slam, his seventh home run of the year.
Mark Ellis started the outburst with a one-out single over the outstretched glove of Seattle shortstop Yuniesky Betancourt. After a five-pitch walk to Johnson, Jack Hannahan fisted an RBI single into left field, scoring Ellis from second base. Daric Barton, who went 2-for-3 with a double and a run scored in his major league debut, then drew another walk, setting the stage for Suzuki.
"I hit it pretty well," Suzuki said. "I kind of watched the reaction of the outfielders to see how far it went."
Blanton, meanwhile, held Seattle at bay until the seventh, when the Mariners plated two runs on four hits. With runners on first and third and two runs already in, Blanton escaped further damage by inducing Seattle's Adrian Beltre into an inning-ending ground out to first after a 12-pitch at-bat.
"That's one of the best at-bats anybody has ever had off of me," Blanton said. "It's one of those at-bats that's fun when you come out on top."
Seattle's Jose Guillen cut the lead to 5-3 in the eighth with a solo home run, his 20th of the season, off Embree. Johnson then iced the game with a ninth-inning grand slam, his 15th homer of the year, off of Seattle's Ryan Rowland-Smith.
"We obviously love home runs ... two of them for eight runs, you can't do much better than that," manager Bob Geren deadpanned. "It was a big day."
Notes: Geren came away impressed with Barton, who was called up Sunday night and collected two hits and two walks in five plate appearances. "Obviously, Daric Barton's debut was all you could ask for," Geren said. "A great debut from a guy we've heard a lot about who's going to be a really nice hitter. He looked all the part tonight." ... Right-hander Rich Harden, on the disabled list since July 8 with a strained shoulder, is expected to throw a simulated game either Wednesday or Thursday, Geren said. ... Meanwhile, injured shortstop Bobby Crosby, on the disabled list since July 24 with a fractured left hand, was cleared to begin baseball activity. "It's possible we may get him back (before the end of the season)," Geren said. "But we may run out of time." ... The A's and Boston Red Sox appear lined up to meet in a Tokyo Dome opener next season, though Gene Orza, the union's chief operating officer, said it's not a done deal yet. A's player representative Huston Street said the club seemed to like the idea. "The team has pretty much approved it," he said before Monday's game at Seattle. "We're just waiting on word."
The Associated Press contributed to this story.
A'S 9, MARINERS 3