Former Galaxy player Alan Gordon headed in the match-winner in the fourth minute of stoppage time for the decisive goal at the Home Depot Center in California.
 
Los Angeles were without stars Landon Donovan and Robbie Keane but had opened a 2-0 lead after 73 minutes on the back of goals to Hector Jimenez and Mike Magee.
 
However, the match changed in favour of the Earthquakes on the hour. Jimenez was sent off after a studs-up tackle on Steven Beitashour, reducing the hosts to 10 men.
 
San Jose took just three minutes to capiltise with Lenhart heading home Marvin Chavez's cross.

They equalised with eight minutes left when David Beckham was adjudged to have handled in the penalty area and substitute Khari Stephenson converted the penalty.

The visitors completed the remarkable comeback in the fourth minute of stoppage time when Gordon found space inside the box to meet Jason Hernandez's cross with a header to seal the dramatic upset.
 
Elsewhere, Justin Meram scored for the third straight game to help lead Columbus to a surprise midweek win over Seattle.
 
Meram opened the scoring 15 minutes in and Emilio Renteria completed the smash-and-grab away win deep in the second half with a tidy volley that condemned Seattle to their second straight home loss.

Other MLS results included the Chicago Fire's 2-1 victory over FC Dallas that earned them the Brimstone Cup, while Chivas USA managed to steal a point at Red Bull Arena with a 1-1 draw against New York Red Bulls.