With the loss, San Jose has now gone 12 games without a win and is looking like a lock to miss out on the playoffs.
Robbie Keane marked his debut with a goal, as he put the Galaxy in front in the 21st minute. Mike Magee secured the win with his injury time goal.
Keane joined the Galaxy earlier in the week from Tottenham Hotspur, signing as a Designated Player. He made an immediate impact, opening his account after 20 minutes.
The Earthquakes dug themselves a massive hole in 81st minute when Steven Beitashour was sent off for reckless play, bringing his team down to ten men.
Los Angeles capitalized on the one-man advantage in stoppage time when Magee eclipsed his mark and redirected a low cross from Sean Franklin to seal all three points.
The Galaxy continue to set the pace in Major League Soccer, earning its league-leading 14th win of the season to remain unbeaten at home. They sit in first place in the Western Conference with 51 points, the most in MLS.
San Jose is heading in the opposite direction, losing four of its last five games. The 'Quakes have managed just 25 points from 25 games this season.
The 'Quakes (5-10-10) will aim to end their winless streak when they travel to BMO Field to face Toronto FC on Aug. 27. The Galaxy (14-3-9) will also be on the road, as they will head to Red Bull Arena to face the struggling New York Red Bulls in a star-studded match on Aug. 28.