After a frustrating first half, the Galaxy secured three points at StubHub Center thanks to goals from Jose Villarreal and captain Robbie Keane in the final 30 minutes.
The hosts would finish the match with 13 shots to seven from Chicago, with five of LA's efforts hitting the target, while the Fire only tested Galaxy goalkeeper Brian Rowe once.
The Galaxy deservedly took the lead in the 65th minute when a defensive mix-up from Jeff Larentowicz and Lovel Palmer allowed a cross to reach Villarreal at the back post, and the left-winger made no mistake with his finish.
Keane clinched the win with nine minutes remaining, volleying a knock-down from Alan Gordon past Sean Johnson.
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