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04/04/12 6:47 PM ET

Donaldson, A's pound Giants in spring finale

Third baseman goes deep twice; Gomes adds solo shot

SAN FRANCISCO -- The A's went long for a trio of home runs -- two by Josh Donaldson -- in the first three innings Wednesday as they pulled away in the final game of the Bay Bridge Series against the Giants, posting an 8-1 victory at AT&T Park.

Donaldson, a career catcher who will start at third base for the A's to begin the season, went 4-for-5 and smacked a two-run shot in the second and a three-run blast in the third. Jonny Gomes added a solo shot in the third, with all the homers coming off Giants Minor Leaguer Yusmeiro Petit, who took the loss.

Starter Tommy Millone was the victor after allowing a run on two hits while striking out three in his two innings of work, but Donaldson was the star of the day for the A's.

"I think today was a fitting end for him and how much work he's done this spring, how much he's had to focus on his defense," A's manager Bob Melvin said of Donaldson. "I think it's all starting to come together right now to where I don't think he's thinking about his defense as much. We really feel good about him being a production guy in our lineup."

The Giants opened the scoring in the first when Buster Posey singled home Pablo Sandoval, who had hit a ground-rule double into the stands in left-center field.

After the A's opened up their lead against Petit, they added a pair of runs in the fifth when Anthony Recker hit a sacrifice fly and Jemile Weeks followed with an RBI single to drive home Donaldson with his third run of the game.

With the outcome of Wednesday's game, Oakland finished their exhibition schedule with a 15-7-2 mark, while San Francisco posted an 18-15-3 record this spring.

Up next: After a Thursday workout, the A's will host the Mariners in their home opener on Friday at 7:05 p.m. PT, essentially continuing the series that began with two games in Tokyo last week. Brandon McCarthy, who took the loss in the opener in Japan despite holding the Mariners to one run in seven innings, will be on the mound for Oakland against Seattle's Jason Vargas.

John Schlegel is a national reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.