Landon Powell hit a tiebreaking home run in the eighth inning, his first homer of the season, and the Oakland Athletics held on to beat the San Francisco Giants 2-1 on Sunday, completing a three-game sweep at home of the defending World Series champs.

Powell, making a rare start in place of catcher Kurt Suzuki, was hitless in two at-bats against San Francisco starter Matt Cain before hitting his first homer of the season off reliever Jeremy Affeldt (1-1).

Trevor Cahill (7-5) pitched eight innings to win for the first time since May 9. Oakland's right-hander, who was 0-5 in his previous seven starts, pitched out of jams in the second and third to help the A's extend their season-high winning streak to five.

Aaron Rowand had an RBI double for San Francisco, which wasted a stellar outing by Cain while losing its fourth straight game overall.

Rookie Jemile Weeks had three hits, his fifth mult-hit game since being called up from the minors on June 7. That helped Oakland complete a 5-1 homestand, the team's best since 2006.

Brian Fuentes pitched a 1-2-3 ninth for his 12th save in 15 chances. Fuentes struck out Cody Ross looking to end the game, and the Giants outfielder angrily reacted.

Powell's homer, only the 10th of his career, spoiled what had been a pitching duel between Cahill and Cain. It also gave Cahill a victory after he was on the hook for a no-decision.

Cahill scattered five hits and had seven strikeouts. He had been 0-5 with a 5.67 ERA in his previous seven starts before putting the clamps on the Giants.

Cain was just as tough but left with his fifth no-decision of the season, ending a three-game winning streak.

Cain gave up a leadoff single to Weeks in the first — the only hit Oakland got until Weeks doubled with one out in the sixth. In between, San Francisco's right-hander retired 14 straight during one stretch, including designated hitter Hideki Matsui, who twice popped out weakly to second.

The A's broke through after Weeks' double, however. The speedy Weeks, called up from the minors on June 7, moved to third on Cliff Pennington's groundout and scored on Coco Crisp's single to right.

Cain allowed only three hits, had five strikeouts and didn't walk a batter for only the second time this season. But with the Giants' offense still sputtering with runners in scoring position (0 for 26 over the last four games), it wasn't enough.

Weeks, who had two of the hits off Cain, has been a big lift to Oakland's lineup. He batted leadoff for the second straight day and collected his fifth multi-hit game to raise his average to .364, leaving the A's in a potential quandary when second baseman Mark Ellis is eligible to come off the disabled list next week. Interim manager Bob Melvin said prior to the game that the situation will "work itself out."

Notes: Cahill's pickoff of Aubrey Huff in the second inning was the A's 15th of the season, tops in the majors. ... All three games in the series were sold out, giving Oakland five for the season. ... Giants IF Mike Fontenot has been slow to recover from a groin strain and might not begin a rehab assignment until next week. ... Oakland RHP Rich Harden (strained right shoulder) will make his first rehab start for Triple-A Sacramento on Monday.