SEATTLE — Danny Farquhar threw the pitches he wanted in the eighth inning Friday night. He did not get the results he expected.
Josh Reddick opened the eighth with a single off Farquhar (1-8), who had just taken over for starter Hisashi Iwakuma. Valencia, who had three hits to break an 0-for-11 slump, followed with his career-high 17th homer deep into the bleachers.
"All you can do is continue to execute pitches, and after that homer I thought I did a good job of it," Farquhar said. "Even the base hit and the home run, I thought I executed those pitches, and that's all you can do."
His 1-2 fastball to Valencia was "about 8 inches above the strike zone" and thrown with the intention of getting him to chase it.
"It was definitely a ball. I told myself to shorten my swing and just punch it. Sometimes you do things and can't explain how it got done," Valencia said.
Picked up off waivers from Toronto on Aug. 3, Valencia has 10 homers and 34 RBIs in 45 games with the A's. That's the most RBIs in franchise history for a player with fewer than 50 games played with the team.
"It was unexpected coming here, but having said that, they gave me the opportunity to play every day," Valencia said. "They put me in the cleanup spot and I've been able to reward them for it."
"I've been playing the past few years waiting for this opportunity and finally it's come. I'm happy to take advantage of it," he added.
Aaron Brooks (3-4), who held the Mariners to six hits and two runs over seven innings, earned the victory.
Sean Doolittle finished in the ninth for his fifth save.
Iwakuma went seven innings. He allowed nine hits and one earned run with eight strikeouts and no walks.
"He threw the ball extremely well, settled down into a nice groove and got us through seven innings," Mariners manager Lloyd McClendon said. "He was fatigued at that point and we had to go get him."
Iwakuma, who finished 9-5, is the fifth pitcher since 1961 to open his career with a .625 winning percentage in each of his first four seasons. He joins Dwight Gooden (1984-91), Roy Oswalt (2001-08), Tim Hudson (1999-2004) and Teddy Higuera (1985-88).
Through the first five innings, the A's had 10 baserunners — seven who advanced into scoring position — and yet managed only two runs.
One scored in the third when second baseman Robinson Cano committed a pair of errors on one play, and another came home on a fielder's choice in the fourth.
"That is what I call alley-ball," McClendon said of the double-error inning. "It is just not acceptable."
Brad Miller had three hits for the Mariners, including his 11th home run, a solo shot in the fifth.
Cano, who said before the game he will have sports hernia surgery later this month, singled in the fifth to extend his hitting streak to a season-high 14 games. He is batting .357 during the streak.
Athletics: Oakland put 23 players on the disabled list this season, up from 18 last year.
Athletics: LHP Sean Nolin (1-2, 5.25 ERA) is 0-1 with a 9.82 ERA over his past two starts. He is 0-1 with a 5.14 ERA in a pair of career starts against Seattle.
Mariners: LHP Roenis Elias (5-8, 3.89) has a 2.05 ERA over his last four starts with just one victory. That's his only win since June 19. Against the A's, he is 1-1 with a 3.44 ERA in four career appearances.