Michael Morse and Brad Miller each had a home run for the Mariners, who saw starter Hisashi Iwakuma (12-6) give up three runs on seven hits and a pair of walks over seven frames.
Coco Crisp and Brandon Moss hit solo shots for the Athletics, who are 2 1/2 games behind the Rangers for first place in the AL West.
A.J. Griffin (10-9) allowed four runs on five hits while fanning seven and walking four over six innings.
"Everything that we did today is what's wrong with us," said A's manager Bob Melvin. "We didn't add on early, we didn't make big pitches when we had to, we didn't come through in situational at-bats. Ugly, ugly game for us and it's been going on for awhile."
Crisp got things going, starting the home half of the first with a home run over the right field wall.
Morse responded with a solo shot with one out in the second.
The A's took the lead again in the fourth. Moss clubbed a 1-1 pitch to left. Yoenis Cespedes' double to center and Josh Reddick's single to right placed runners at the corners, before Alberto Callaspo plated Cespedes with a sacrifice fly.
However, Miller answered in the fifth with a solo shot to make it a 3-2 game.
"You just try to see something up," Miller said. "He (Griffin) kind of got to me take some weak swings, so I was trying to get a good hack at him. You just try to scrap and stay in the ballgame and hopefully, you can win it late."
An inning later, Kendrys Morales walked to start the inning. After Justin Smoak and Morse struck out, Dustin Ackley drew a walked. Ryan then delivered a two-RBI double down the left-field line for a 4-3 lead. As Ackley scored, he collided with catcher Stephen Vogt to beat the throw to the plate. He slid into Vogt's legs, knocking him backwards and on his back. Both players continued playing.
Seattle extended its lead even further in the eighth. With runners at the corners, Ryan hit a blooper up the middle, scoring Smoak.
Danny Farquhar struck out the side in the ninth to notch his ninth save.
Seattle has homered 150 times this season, tied with Toronto for second-most in MLB ... Ryan entered the game batting .120 over his last 27 games ... Morse is 6-for-9 with two home runs and two RBI against Griffin ... The Mariners lead the season series 10-6 with three games remaining. Over the last seven seasons, they have won the season series in odd-numbered years (2007, 2009, 2011) ... Crisp has not committed an error in 80 games in the outfield and has a 108-game errorless streak, dating back to Aug. 23, 2012 ... Both teams have an off day Thursday.
08/21 23:46:36 ET