The 40-year-old Colon (10-2) tossed eight solid innings in Friday's opener of the three-game series, with his lone blemish coming in the form of rookie Nick Franklin's three-run homer in the third.
Colon gave up seven hits, walked two and struck out four to extend his longest personal winning streak since a career-high eight-game run from July 21-Sept. 10, 2005.
"He knows how to pitch. He does as good a job with his fastball as any guy in the league," Mariners manager Eric Wedge said of Colon.
Grant Balfour closed the door in the ninth to earn his 18th save.
Franklin's shot gave Seattle a 3-2 lead, but Jed Lowrie and Coco Crisp led off the fourth and sixth innings with home runs off Mariners starter Hisashi Iwakuma (7-3) to put the Athletics in front.
Cespedes then provided some insurance in the ninth with his second two-run blast of the night, this one off reliever Tom Wilhelmsen. The slugging Cuban also took Iwakuma deep with two outs in the first.
"Cespedes kind of bookends us, one in the first and one in the ninth, and both were huge," Oakland manager Bob Melvin said. "One gave us a lead and the other extended the lead, made it a little easier on us in the end."
Colon became the third pitcher in Oakland history to win 10 games as a 40- year-old ... The last A's pitcher to win seven or more consecutive starts was Barry Zito, who won eight straight from June 28-Aug. 4, 2005 ... Balfour has converted each of his last 36 save chances ... The A's had dropped five of their last seven games ... Lowrie ended his career-high 62-game home run drought ... Iwakuma allowed six hits and fanned six over seven innings ... The Mariners lost their third straight game.
06/22 02:54:59 ET