OAKLAND, Calif. -- Oakland A's rookie Sean Manaea knew he was on a pitch count Wednesday night when he came off the disabled list to make his 10th career start, so he made quick work of the San Francisco Giants.

Manaea (3-4) pitched 5 2/3 shutout innings in a 7-1 victory against the Giants at the Oakland Coliseum. The left-hander, who had been on the DL since June 14 with a strained left forearm, allowed six hits, struck out four and walked only one, Manaea exited after allowing a two-out double to Buster Posey in the sixth on his 83rd pitch -- two shy of his limit -- with the A's leading 7-0.

"I felt great," Manaea said. "I was kind of worried before the game about my forearm, but as the game went on I didn't feel a thing."

Jed Lowrie and Yonder Alonso each hit a two-run homer for the A's, who beat the Giants for the third straight time and will try to sweep the four-game season series on Thursday night at the Coliseum.

The way Manaea was pitching, he didn't need much offensive support.

"That was dominating stuff," A's manager Bob Melvin said. "That's the stuff you've heard about when the name Sean Manaea came up, made the trade, going through the minor leagues, doing that type of thing. I know he felt good about it. So did we."

Giants right-hander Jake Peavy (4-7) gave up seven runs -- just three of them earned -- on five hits over 3 1/3 innings. He walked two, struck out none and allowed two home runs, but he was hurt by three Giants errors.

"It was certainly a frustrating night just on all fronts," said Peavy, who had won three of his previous four starts and allowed a combined eight earned runs in his previous six starts. "We didn't play our best. Just one of those nights. Not fun to endure.

"Obviously we made some mistakes and it's a team game. You have to pick your teammates up, and I certainly didn't do what I could."

The A's won for the sixth time in seven games, scoring 53 runs during that span.

"It's great to get these runs in bunches but to win over the course of the season you have to be able to consistently put up runs," Lowrie said. "That doesn't mean scoring 13 in one game and seven the next. It's being able to manufacture runs, get guys on, get them over, get them in. That's how you're going to consistently win games."

Coco Crisp went 2-for-4 with a triple, an RBI and a run for the A's.

Posey went 3-for-4, while Brandon Crawford had one hit in three at-bats and drove in a run in the eighth with a sacrifice fly for the Giants, who lost for the fourth time in five games.

The A's took a 3-0 lead in the third inning, scoring three unearned runs off Peavy.

With one out, Marcus Semien hit a pop up to shallow right field that dropped when second baseman Ramiro Pena collided with right fielder Mac Williamson. Pena was charged with an error, and Semien wound up on third base.

Pena, starting in place of Joe Panik (concussion), appeared to hurt his left ankle. However, he stayed in the game until being replaced for a pinch hitter in the fifth.

"He's pretty sore," Giants manager Bruce Bochy said. "X-rays were negative. We'll get an MRI tomorrow. He's looking at (missing) 5-7 days. I think it's pretty evident we're going to have to get somebody to help out here."

Billy Burns brought Semien home with a sacrifice bunt down the first base line, and Crisp followed with a triple to the left-center gap.

Lowrie made it 3-0 with a home run down the right-field line that went in and out of a leaping Williamson's glove and landed over the fence. The blast was Lowrie's second of the season and came on a 3-2 pitch.

The Giants loaded the bases with one out in the fourth, but Manaea got Williamson to ground into a double play with a 3-2 count, one pitch after he lined a shot just left of the foul pole in left field. After escaping that jam, Manaea pumped his fists twice as he headed toward the dugout.

"Just being in that moment and getting those big outs, that was huge," Manaea said. "All the emotions I had just let out. It was awesome."

The A's added four runs in the fourth, extending their lead to 7-0. After Butler walked with one out, Alonso sent Peavy's first pitch into the right-field seats for his second home run of the season.

Semien sent a deep fly to left-center left fielder Angel Pagan misplayed for a three-base error, and Burns drove him in with a double to left that got past Pagan. Crisp followed with an RBI single.

NOTES: Giants 2B Joe Panik was placed on the seven-day concussion disabled list, retroactive to Tuesday. Ramiro Pena started at second base Wednesday against the A's. ... The Giants purchased the contract of INF Ruben Tejada from Triple-A Sacramento, and the former Mets shortstop started at third base. ... A's LF Khris Davis was a late scratch because of a left shoulder contusion. Davis was hurt Tuesday in the first inning when he slammed into the outfield wall in San Francisco trying to catch 1B Brandon Belt's double. ... Oakland INF/OF Arismendy Alcantara was optioned to Triple-A Nashville. ... LHP Eric Surkamp was claimed off waivers from Oakland by the Texas Rangers. ... Giants RHP Sergio Romo (right flexor strain) will make rehab appearances Thursday and Friday with Triple-A Sacramento.