Chris Schuler's 102nd-minute strike lifted Real Salt Lake to a 2-0 victory over Los Angeles Thursday, ending the Galaxy's quest for a third straight MLS Cup crown on Thursday.
Los Angeles went into the second leg of the Western Conference semi-final tie with a 1-0 lead, but Sebastian Velasquez put Salt Lake in front 35 minutes in.
That score stood up through regular time, and with the aggregate score knotted at 1-1 the match went to extra time.
Schuler emerged as the hero, sliding in to stab home a free-kick from Javier Morales in the 102nd. Real Salt Lake held on for the 2-0 victory and a 2-1 aggregate triumph.
The Galaxy had lifted Major League Soccer's ultimate prize the past two seasons - both times with the help of now-retired David Beckham.
Real Salt Lake next face the Portland Timbers, who advanced with a 3-2 second-leg victory over Seattle on Thursday. Portland had won the first leg 2-1.
The Eastern Conference finals will pit the Houston Dynamo against Sporting Kansas City on Saturday.
Houston end Red Bull's charge
Houston notched a 2-1 second-leg victory over the New York Red Bulls on Wednesday for a 4-3 aggregate triumph. Houston advanced to their third straight Eastern Conference final.
It was a disappointing end to the season for Thierry Henry's New York, the top seeds in the East and winners of the Supporters' Shield as the team with the best regular-season record.
Sporting Kansas City advanced with a 4-3 aggregate victory over the New England Revolution, sealed with a 3-1 second-leg win on Wednesday.
The MLS Cup final will be played between the East and West champions on 7 December, on the home pitch of the contender with the best regular-season record.