Oakland (75-85) has lost four straight and will finish in third place in the AL West for the second straight year.

In his last eight outings, Rowland-Smith has a 2.56 ERA, allowing three runs or fewer each time out.

"He was out there today with total focus, preparation and he's just getting better and better and I think it's a real bright spot for the organization that he's come on like he has," Mariners manager Jim Riggleman said.

Rowland-Smith has been the surprise of the rotation on a team that traded during the offseason for Erik Bedard, has a budding ace in Felix Hernandez and a former first-round draft choice in Brandon Morrow.

After starting the season as a reliever, Rowland-Smith was sent down to Triple-A Tacoma on July 25 to be converted into a starter. After three starts, he returned to Seattle.

"It's been a huge learning experience for me and I've had success in the mean time," Rowland-Smith said. "I'm really happy with what I've done."

He has likely pitched himself into Seattle's starting rotation for 2009.

"There is nothing more he can do except come to spring training ready to nail his spot down," Riggleman said. "As far as composure and competitiveness, he's where he needs to be. He just needs to fine tune his pitching a little bit and you're going to have a heck of a pitcher."

The Mariners offense provided Rowland-Smith with plenty of run support, and Sean Green allowed one hit over the final 2 1-3 innings for his first career save.

The Mariners loaded the bases with no outs in the first inning. After Oakland starter Greg Smith walked in a run, Wladimir Balentien doubled to left-center field to score two runs. Kenji Johjima followed with his drive over the left-field wall to make it 6-0.

Daric Barton led off the second with a double and scored on Cliff Pennington's single. The A's picked up another run in the top of the fourth. Pennington doubled to lead off the inning and advanced to third base on a wild pitch by Rowland-Smith. Travis Buck beat out a throw by third baseman Matt Tuiasosopo for an infield single that scored Pennington.

Smith (7-16) didn't allow another hit after the first until Yuniesky Betancourt doubled in the fifth. Smith allowed five hits in seven innings.

"He pitched better after the first inning," A's manager Bob Geren said. "The change up, the home run, was up, the curve ball was up. Then he started getting the ball down in the zone with movement."

Notes: The six-run first inning by the Mariners was their biggest since jumping out to a 9-0 lead over the Detroit Tigers on July 30, 2003. ... Green is the 10th pitcher for Seattle this season to record a save. ... Brandon Morrow and Rowland-Smith earned the win in each of the last two games for Seattle, marking the first time starters earned back-to-back victories since Jarrod Washburn, Carlos Silva and Erik Bedard won three consecutive games June 27-29, at San Diego. ... Smith picked off Betancourt in the second inning for his 16th pickoff of the year. It tied a major league record along with Charlie Hough, Charlie Liebrandt and Terry Mulholland for most pickoffs in a single season. "If I'd picked a couple guys off in the first inning, that would've been a great time to do it," Smith said.