SEATTLE -- Dan Johnson's extra work paid off.
Known for his power numbers in the minors, Johnson hit .273 with five doubles and just four RBI in 21 games since being called up from Triple-A Sacramento on May 27. In his first at-bat against Joel Pineiro (2-4) in the third, the 25-year-old first baseman hit a 1-0 pitch 418 feet into the right-field seats.
"It's one of those things I've always been able to hit home runs, then I get here and the ball sinks a little more," Johnson said. "I haven't adjusted to it yet. But tonight I got the head out on a good pitch to hit and finally got the monkey off my back."
Oakland manager Ken Macha and hitting coach Dave Hudgens worked on Johnson's swing before the series opener Monday night.
"(Macha) has asked why I haven't been driving the ball as in the past," said Johnson, the MVP of the Pacific Coast League last year. "It has been the biggest learning experience I've ever been through in baseball. Coming through the ranks I've always had a period of adjustment.
"The ball moves so much here when these guys let it go, it's tough to adjust to. I was used to seeing four-seam fastballs every at-bat. Now it seems they don't exist anymore."
The Athletics won their fourth straight -- matching a season high -- and eighth in their last 11.
Harden (3-3), who had not pitched since straining his left oblique muscle May 13, allowed just two hits for his first win since April 21. He walked one and struck out three.
Justin Duchscherer got the final five outs for his third straight save.
Pineiro gave up all four runs and eight hits in eight innings to pick his first decision in seven starts. He walked four and struck out six.
Richie Sexson doubled off the center-field wall to open the second inning, moved to third on Raul Ibanez's grounder and scored on Jose Lopez's sacrifice fly to give the Mariners a 1-0 lead.
"He has outstanding stuff," Mariners manager Mike Hargrove said of Harden. "I don't know that there is anybody else in our league that has better stuff than this guy."
The A's took a 2-1 lead in the third, started by Johnson's homer. Marco Scutaro then walked with one out, moved to second on Jason Kendall's single and came home on Mark Kotsay's run-scoring single.
Oakland also scored twice in the fourth. Scott Hatteberg opened with a single down the right-field line and advanced to third on Bobby Kielty's double past first baseman Sexson into the right-field corner, and scored on Johnson's sacrifice fly to left field. One out later, Scutaro's RBI single to center drove in Kielty from second to make it 4-1.
Harden got into a two-out jam in the fifth after Reed's single into shallow right. After Mike Morse walked, Pat Borders sent a long drive into right-center that Kotsay ran down at the warning track after a long run to end the inning.
"I don't even know which way he turned his glove on that thing," Macha said of Kotsay's catch. "But when I heard the dead silence I knew he caught it."
The Mariners pulled within 4-2 on Adrian Beltre's RBI single in the eighth but Richie Sexson hit into inning-ending 5-4-3 double play. He also did the same thing in the sixth.
"Anything is better, a strikeout, flyout, anything is better other than what I did twice," Sexson said. "That's my job. I didn't get it done tonight. I hope I get a couple chances tomorrow and try it again."
Mariners rookies, shortstop Morse, center-fielder Reed and catcher Rene Rivera, along with second-year second baseman Lopez have combined to hit .324 in June. ... Johnson hit .299 with 29 home runs and 111 RBI for Triple-A Sacramento last season.