Donovan got his first goal in the 23rd minute, handing the Galaxy a 2-0 lead, then made it 4-0 with another tally in the 41st. His second goal gave him 134 in his MLS career, tying him with Jeff Cunningham for the all-time mark.
Donovan also assisted on one of Robbie Keane's two goals as Los Angeles (14-11-6) snapped a four-game winless streak and helped their chances for a Western Conference playoff spot.
Gyasi Zardes added a goal for the Galaxy.
Last-place Chivas USA fell to 6-18-8.