OAKLAND, Calif. -- The Oakland Athletics weren't known for their power last season when they hit 169 homes, fewer than all but three other American League teams.

The A's, apparently, have rediscovered the long ball this year. They hit two more home runs Friday night, solo shots by Trevor Plouffe and Yonder Alonso, powering them to their fourth straight win, a 3-1 victory against the Seattle Mariners at the Oakland Coliseum.

The A's have 22 homers in only 17 games. Plouffe, who signed with the A's as a free agent in January, hit his 100th career home run in the fifth inning, tying the game 1-1 with a shot to center field. The home run was his fourth of the season, all in the past seven games. He had a three-run shot against Seattle in a 9-6 victory Thursday night.

"It's good," Plouffe said of the A's power. "We saw it in spring training. We've got some guys ... we're not trying to go up there and hit homers but we're trying to have good at-bats, trying to hit the ball hard. I know Yonder made a swing adjustment this year with the leg kick and we've seen the benefit of that and (Khris Davis) has been doing what he always does. We feel like we have a long lineup and it's starting to show."

Davis, who had 42 homers last year, already has seven. Alonso has three home runs.

Left-hander Sean Manaea (1-1) held the Mariners to one run on five hits over six innings. He struck out six, walked three and threw 96 pitches. With two runners on and two outs in the top of the sixth, he struck out Taylor Motter to end his final inning, preserving a 1-1 tie.

The A's scored twice in the bottom of the frame, giving Manaea his first win of the season. In his previous start against Houston, he allowed no hits through five innings but walked the bases loaded in the sixth and was pulled after the next batter reached on an error. Manaea had a no-decision in a 10-6 loss.

"It was huge," Manaea said of getting through the sixth. "After that inning, we had the momentum on our side, and throughout a baseball game, momentum is huge, and it can sway a game very easily. Getting out of that inning was huge, and the offense put up a two-spot. Overall, it was a great game. We're playing really good baseball right now."

Mariners right-hander Hisashi Iwakuma (0-2) gave up three runs on five hits, including two home runs, over 5 1/3 innings. He struck out three and walked four.

"They got to those pitches," Iwakuma said of the home runs. "Especially the slider that was up in the zone to (Plouffe) and the other home run to Alonso was up and in, but he put a good swing on it. Tip your cap. Those are the pitches that cost us the game."

Alonso crushed Iwakuma's first pitch of the sixth inning high and deep over the right-center field wall, putting Oakland ahead 2-1.

Jed Lowrie followed with an opposite-field double to left-center and moved to third on Khris Davis' ground out. Stephen Vogt brought Lowrie home with a sacrifice fly to make it 3-1.

"Yonder's homer was huge, but the sac flay was just as big," A's manager Bob Melvin said.

Ryan Dull pitched a scoreless seventh inning, Sean Doolittle a perfect eighth and Santiago Casilla a one-two-three ninth for his third save.

Seattle took a 1-0 lead in the first when Guillermo Heredia lined a two-out single to center and scored on rookie Mitch Haniger's triple into the left field corner. It was Haniger's first triple, 10th extra-base hit and 16th RBI.

"We did not swing the bat well tonight," Mariners manager Scott Servais said. "Manaea had pretty good stuff. We had a couple of opportunities, but we didn't string any good at-bats together. Offensive we're just not getting it clicking. You've got to hit to win on the road and we haven't."

NOTES: Oakland center fielder Rajai Davis missed Friday night's game a left hamstring injury. ... Mariners right-handed reliever Dan Altavilla was optioned to Triple-A Tacoma. Seattle recalled right-hander Chase De Jong from Tacoma. ... A's right-hander Cesar Valdez was optioned to Nashville, one day after being called up and making his first major league start and appearance since 2010. Oakland recalled first baseman/right fielder Matt Olson from Nashville. ... A's right-hander Kendall Graveman (strained right shoulder) threw a bullpen session Friday and appears to be on track to come off the disabled list on Tuesday, the first day he's eligible, or soon after. ... Mariners shortstop Jean Segura (right hamstring) began a rehabilitation stint with Double-A Arkansas on Friday night and should need only one or two more games before being activated with the Mariners, manager Scott Servais said.