SEATTLE -- The Oakland Athletics spoiled Hisashi Iwakuma's return to Safeco Field, hammering the Seattle starter for six hits and seven runs in the fifth inning on the way to an 11-5 win over the Mariners.

Third baseman Danny Valencia gave Oakland its first lead with a two-run homer in the fifth inning, and the Athletics rallied from a five-run deficit to frustrate Iwakuma in his first home start since he threw a no-hitter Aug. 12.

"I think he would admit he didn't have his best stuff," Valencia said after the A's used the seven-run fifth to hand Iwakuma his first loss since July 28. "He left some pitches up, and we made some good swings on him."

Iwakuma (5-3) gave up seven runs on seven hits in 4 2/3 innings, with almost all the damage coming in the fifth.

"He was in the middle of the plate, he elevated some pitches, and they took advantage of it," Seattle manager Lloyd McClendon said of the key inning.

Oakland right-hander Edward Mujica (3-4) earned the win after pitching two scoreless innings of relief. The A's had to use five pitchers because starter Felix Doubront took a line drive off his foot in the first inning and lasted just two innings. Switch pitcher Pat Venditte threw two hitless innings before Drew Pomeranz fired a perfect ninth.

The A's had 15 hits in the win, including home runs by Josh Reddick and Valencia. Reddick hit his 15th homer of the season with two outs in the top of the ninth. Oakland ended up scoring three runs with two outs in the ninth, with second baseman Brett Lawrie adding a two-run double.

Reddick and catcher Stephen Vogt each had three hits for Oakland, which got 14 hits from the top six batters in its lineup.

"The at-bats were good, led to another at-bat and got better as the game went on," Oakland manager Bob Melvin said. "Not only did we have the seven-run inning, but (we) added on after that. One of our better games of the year."

Shortstop Ketel Marte had three hits and a stolen base for Seattle. The Mariners allowed six or more runs for the fifth consecutive game.

Oakland, which entered the fifth with just one hit, sent 11 batters to the plate while piling up seven runs on seven hits and a walk in the inning. Vogt had two doubles in the rally, while center fielder Billy Burns and first baseman Mark Canha had back-to-back, two-run doubles to pull the A's within 5-4.

A mental gaffe by Seattle's Jesus Montero with two outs allowed Oakland to tie the score 5-5. With Canha on second base and two outs, Reddick grounded to first base and ended up beating Montero to the bag when the Mariners first baseman opted not to toss to Iwakuma covering first. Canha came around to score on the play, which was ruled an infield single, tying the game at 5-5.

"Montero didn't quite get that play right at first base, and that hurt us a bit," McClendon said. "It opened up the floodgates."

Valencia hit a two-run homer on the next at-bat to give Oakland (55-71) its first lead of the game while chasing Iwakuma.

"We were very resilient," Valencia said. "We fight and take advantage of small mistakes and do the little things, and that's what we did tonight."

Doubront lasted only two innings due to a bruised right foot he sustained when Seattle second baseman Robinson Cano hit a low liner off his shoe in the first inning. Doubront collapsed in the dirt but eventually got up and continued to pitch.

"I said, 'If it's not broken, I can keep pitching,'" Doubront said, "but it was affecting my release point. I was pretty mad about coming out, but I understood."

He ended up throwing 40 pitches, allowing four hits but no runs. It marked the second day in a row that an Oakland starter had to leave a game due to injury, as Sunday starter Kendall Graveman sustained an oblique injury that eventually landed him on the disabled list.

Home runs by designated hitter Franklin Gutierrez and left fielder Mark Trumbo highlighted a five-run third inning as the Mariners jumped out to a 5-0 lead after Oakland reliever Evan Scribner replaced Doubront.

Cano drove in the game's first run with an RBI single, and then Gutierrez hit a three-run homer to center field, giving the Mariners a 4-0 lead. Two batters later, Trumbo hit his eighth home run as a Mariner, a solo shot.

The Mariners (57-68) survived their own injury scare in the third, when star right fielder Nelson Cruz took a pitch from Scribner off the inside of his right elbow. Cruz was in obvious pain and received attention from a team trainer and McClendon before deciding to stay in the game.

NOTES: The A's fired third base coach Mike Gallego and replaced him with former Texas Rangers manager Ron Washington. Washington, 63, was coaching infielders for Oakland in recent weeks but was not on the field for games. ... Seattle commemorated RHP Hisashi Iwakuma's no-hitter on Aug. 12 by giving out T-shirts to fans attending the game Monday. ... Oakland's Felix Doubront was the fifth consecutive left-handed starter to face the Mariners. The streak is supposed to end Tuesday, when Oakland RHP Jesse Chavez is scheduled to start. ... The A's recalled INF Max Muncy from Triple-A Nashville and placed RHP Kendall Graveman on the 15-day disabled list. Graveman had his Sunday start aborted after six innings because of a strained oblique muscle.