OAKLAND, Calif. -- Guillermo Moscoso was more worried about shutting down Seattle than his status in Oakland's rotation.

Moscoso made a strong case to keep his spot by allowing two hits in seven innings and Scott Sizemore homered to help the Athletics salvage the finale of a three-game series with a 2-0 victory over the Mariners on Wednesday.

"Like I said before the game. I have to be focused today and not worry about if this would be my last start," Moscoso said. "I just had to stay focused and make quality pitches today and give the team a chance to win. That's what we're looking for."

Sizemore hit a solo homer in the second inning and added an RBI single in the fifth against Jason Vargas (6-6) to give Moscoso (3-4) more than enough support to win for the first time since May 29.

Moscoso won his first two starts before going 0-4 in June, despite posting a 2.25 ERA. Despite the solid performance, Moscoso's spot in Oakland's rotation is in jeopardy with Tyson Ross expected to come off the disabled list following the All-Star break.

"I just have to do my best, keep doing my best and try to stay deep into games and give the team a chance to win," he said. "Any role, starter or reliever. I'm just trying to stay here as long as I can."

Moscoso made a strong case to remain in Oakland's starting five, allowing only singles to Dustin Ackley in the second inning and Adam Kennedy in the seventh. Moscoso struck out five, walked one and got 13 of his outs in play on flyballs.

Moscoso has allowed just one earned run in his past 24 2/3 innings, lowering his ERA to 2.16.

"Every time out he's been that strong," closer Andrew Bailey said. "I wouldn't say today is his best but it's definitely one of them. Everything he's asked to do he's done, whether it's bullpen or start. Each and every time out he's made the most of the opportunity. It's going to be a tough decision. That's what you want. You want the front office to have to make a tough decision. That means you're pitching well and playing good baseball."

Joey Devine pitched a perfect eighth and Bailey finished for his eighth save in nine chances.

The Mariners managed just two hits and had their three-game winning streak snapped.

"We just didn't put a lot of pressure on him," DH Adam Kennedy said of Moscoso. "You look at his numbers and he's a fly-ball pitcher but we should be able to make adjustments. We just didn't get it done today."

The A's lost the first two games between the AL's lowest-scoring teams in predictably tight fashion. Seattle won the opener 2-1 behind a strong start by Michael Pineda and then won 4-2 Tuesday with help from a throwing error by Oakland shortstop Cliff Pennington in the 10th inning.

Sizemore got the A's started in the first inning when he turned on a first-pitch fastball from Vargas and drove it into the left-field seats for his third homer of the season to make it 1-0.

Oakland added a second run in the fifth inning when Pennington reached second on an infield single and throwing error by shortstop Brendan Ryan. He moved to third on a balk and scored on Sizemore's two-out hit to center field.

Vargas allowed two runs and five hits in eight innings for his fourth complete game in his past seven starts.

"Sizemore got him a couple times but Jason threw the ball well again, gave us every opportunity to win the ballgame," manager Eric Wedge said. "You can't say enough about how consistent he's been. He was efficient all day long."

Game notes
The Mariners matched a season-worst with three errors, having also done it April 6 at Texas. ... Oakland reliever Grant Balfour (right oblique) felt good after a one-inning rehab assignment Tuesday and will be activated from the DL on Thursday. ... OF Josh Willingham also might be ready to return Thursday from a strained left Achilles. ... The Mariners called up infielder Kyle Seager from Triple-A Tacoma after the game and designated catcher Jose Yepez for assignment.