The Galaxy regained a share of the lead in the MLS standings with Western Conference rival the Seattle Sounders after stretching their undefeated run to nine games.
Keane opened the scoring with a chip from Donovan's cross in the eighth minute and finished the scoring in the 82nd minute, beating goalkeeper Luis Robles for his 17th goal of the season.
Donavan scored Galaxy's second goal from close range in the 50th and gave the last pass for Gyasi Zardes' goal the 69th minute. It was Donovan's 134th career assist, one short of Steve Ralston's MLS record.
At Houston, Omar Cummings and Boniek Garcia scored as the hosts beat Chicago 2-0 to remain alive in the Eastern Conference playoff race.
Houston is eighth in the conference, with only the top five making the playoffs.
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