OAKLAND, Calif. -- The Seattle Mariners never had much success against Oakland A's ace Sonny Gray prior to Tuesday's game at the Oakland Coliseum.

Gray was 4-1 with 2.14 ERA in nine career starts vs. Seattle.

This time, the Mariners struck back. Leonys Martin launched a two-run homer off Gray in the second inning, and Robinson Cano added a solo home run in the third, sparking an 8-2 victory.

Gray (3-3) gave up seven runs on 11 hits in seven-plus innings, and Kyle Seager added a three-run blast off reliever Marc Rzepczynski in the eighth.

"We got good pitches to hit," Mariners manager Scott Servais said. "Sonny maybe wasn't quite as sharp as we've seen in the past, but give credit to our guys. Robby had good swings, Seager had a big night."

Cano hit his ninth homer of the season and moved into a tie with Toronto's Josh Donaldson for the American League lead. He went 2-for-4 with a double and two runs. Seager had two hits, including a double. Ketel Marte, Steve Clevenger and Martin also had two hits apiece in a 13-hit Mariners attack.

"It's a good group," Seager said. "Top to bottom offensively, everybody's swinging the bat pretty well."

Right-hander Hisashi Iwakuma pitched seven strong innings for his first victory of the season, and the Mariners clinched their sixth consecutive series win, taking the first two games of their three-game set against Oakland. They beat the A's in Oakland for the sixth straight time and moved into first place in the American League West at 15-11, a half-game ahead of Texas (15-12).

Iwakuma (1-3) gave up one run on four hits, striking out three and walking two. In his first five starts, he went 0-3 with a 4.65 ERA.

"I think I had a lot of life on the fastball, especially down low in the zone that was very effective," Iwakuma said. "I was able to get strike one, get ahead early, and that worked out well for me."

Gray struck out six and walked one but had his second straight rough start. In his previous outing, he had the shortest start of his career, giving up four runs over two innings in a 9-4 loss to the Detroit Tigers.

"I thought I threw the ball well," Gray said. "That's the best I've felt all year. It's just unfortunate the way it turned out. I threw more strikes, attacked guys. I pitched into the eighth and come out with a bad start. It was a really weird game."

A's left fielder Khris Davis hit his sixth home run of the season and third in two days, a solo shot in the ninth off Steve Johnson, who made his Mariners debut.

Iwakuma didn't give up a run until the sixth inning, when Billy Burns grounded a leadoff single to left, stole second base and scored on Jed Lowrie's single, cutting Seattle's lead to 3-1.

Seattle answered with a run in the seventh and four in the eighth, three of them on Seager's long home run into the right field seats.

The Mariners took a 2-0 lead in the third inning on Martin's towering two-run shot into the right field stands. Clevenger grounded a single to center with one out for Seattle's first hit of the game.

Martin, who came into the game batting .169 and hits ninth in the Mariners' order, launched Gray's 0-1 curveball for his fifth home run of the season.

"His stuff was good at times," A's manager Bob Melvin said of Gray. "He made the one bad pitch to Martin. Cano hit a good pitch out to left. He had movement, was down in the zone. It just got a little out of hand."

Cano made it 3-0 with a leadoff homer in the fourth, going the opposite way and sending Gray's first-pitch changeup over the left field wall.

"Middle away, you're going to go with the pitch," Cano said.

NOTES: Mariners RHP Tony Zych (sore right shoulder) was placed on the 15-day disabled list. He returned to Seattle and will be examined by team doctors. ... Seattle purchased the contract of RHP Steve Johnson from Triple-A Tacoma. Johnson had a 2.25 ERA over 16 innings of relief for Tacoma with 20 strikeouts and two walks. ... A's 3B Danny Valencia (hamstring) went 0-for-3 Monday night for Class A Stockton in his first game of a rehab assignment. He took batting practice with the A's on Tuesday and will play another rehab game with Stockton on Wednesday. He appears to be on track to be reinstated Friday at Baltimore, the first day he's eligible. ... A's 2B Jed Lowrie, who is nursing a sore calf, started Tuesday after being out of the lineup Monday.