Donaldson's HR, Straily's strong start lead A's past Giants 4-1 in Bay Bridge Series opener

Oakland Athletics' Josh Donaldson scores after hitting a 2 run home run against San Francisco Giants starting pitcher Madison Bumgarner during the fourth inning of a baseball game in Oakland, Calif., Monday, May 27, 2013. (AP Photo/Tony Avelar) (The Associated Press)

Oakland Athletics starting pitcher Dan Straily throws to the San Francisco Giants during the first inning of a baseball game in Oakland, Calif., Monday, May 27, 2013. (AP Photo/Tony Avelar) (The Associated Press)

OAKLAND, Calif. – Josh Donaldson hit a two-run homer to back Dan Straily's strong start, and the Oakland Athletics beat the San Francisco Giants 4-1 in the Bay Bridge Series opener Monday.

Straily (3-2) tossed six innings of one-run ball, allowing four hits and one walk. Buster Posey's groundout in the sixth inning drove in San Francisco's lone run.

Donaldson connected against Madison Bumgarner (4-3) in the fourth, and Yoenis Cespedes added a two-run double against George Kontos in the seventh to extend Oakland's lead.

Sean Doolittle pitched two perfect innings and Grant Balfour recorded his 11th save of the season for Oakland, which has won four straight and nine of 10.