Bartolo Colon worked seven strong innings to win his sixth straight decision, Josh Reddick homered and matched a career high with four hits, and the
Sean Smith and Brandon Moss each homered and drove in two runs for the Athletics, who moved three games ahead of Texas in the AL West their largest lead since ending the 2006 season four games up. Josh Donaldson also went deep, and Yoenis Cespedes, Coco Crisp and John Jaso each drove in runs for Oakland.
Colon (9-2) allowed two runs on eight hits, did not walk a batter and struck out three to extend his home win streak to seven.
Iwakuma (7-2) lost for the first time since April 23, giving up four runs on a season high-tying eight hits. He also walked Jaso three times and struck out three. Iwakuma's streak of not allowing an earned run was stopped at 31 2-3 innings, second longest in Mariners' history to Mark Langston's 34-inning streak in 1988.
Endy Chavez had two hits and drove in two runs for the Mariners, who were looking for their first sweep of the season.
Michael Morse, Jason Bay and Mike Zunino each singled to open the second inning for Seattle. After Colon struck out Brendan Ryan, Chavez delivered a two-run single. Nick Franklin singled to reload the bases, but Colon got Kyle Seager and Kendrys Morales on short fly balls to limit the damage.
Iwakuma allowed his first earned run since May 26 when the A's got to him in the fourth. Donaldson and Smith hit back-to-back doubles to open the inning and Reddick followed with an RBI single.
Cespedes and Moss each drove in a run in the fifth to make it 4-2.
Colon slammed the door on the Mariners after the second, retiring 11 straight before allowing Morse's single in the sixth. Colon induced a double play ball from Bay and then worked a perfect seventh.
A's pitchers faced the minimum over the final seven innings.
Donaldson and Smith hit back-to-back home runs with one out in the seventh against Blake Beaven. Crisp later walked with the bases loaded and Jaso hit a sacrifice fly against Tom Wilhelmsen to make it 8-2.
Moss and Reddick each went deep in the ninth against Carter Capps.
Sean Doolittle and Dan Otero pitched an inning apiece to close it out.
Notes: Mariners LHP prospect Danny Hultzen (rotator cuff strain) remains at extended spring training. The former first-round draft pick last appeared in a game on April 19 with Triple-A Tacoma. Manager Eric Wedge said before the game that Hultzen would remain in Peoria while he continues to build arm strength. ... A's INF Jed Lowrie was given the day off as manager Bob Melvin continues to deal with the effects of Thursday's 18-inning game against the New York Yankees. ... Cespedes will likely return to the outfield when the A's open a four-game series at Texas on Monday. ... Colon threw 31 pitches in the second inning, the first time he's thrown 30 or more in an inning this year. ... INF Justin Smoak (strained right oblique) could return to the Mariners lineup as early as Monday night in Anaheim. ... The A's hit more than two home runs in a game at home for the first time this year. ... RHP Aaron Harang (3-6, 5.60 ERA) takes the mound for Seattle against the Los Angeles Angels on Monday. He threw a two-hit shutout in his last start. ... The A's will send RHP Dan Straily (4-2, 4.45) to the mound against the Rangers. He's 3-0 with a 2.21 ERA over his last five starts.