Victor Bernardez struck a last-gasp winner as San Jose Earthquakes secured a narrow first-leg lead over Los Angeles Galaxy in the Western Conference semi-finals.
The Honduran defender beat goalkeeper Josh Saunders with a low free kick in the fourth minute of added time.
Galaxy had earlier gone close to breaking the deadlock when Robbie Keane rattled the crossbar in the 85th minute.
San Jose have now scored nine goals in stoppage time this year, six of which have been match winners.
The second leg takes place on Thursday.
