Cole Grossman's stoppage-time equalizer allowed 10-man Real Salt Lake to escape Jeld-Wen Field on Wednesday with a 3-3 draw against the Portland Timbers.
Kalif Alhassan thought he had won the game for Portland with a goal in the 86th minute that broke a 2-2 deadlock.
However, the Timbers defense failed to clear a ball inside the penalty area in stoppage time, allowing Grossman to roll a shot past diving goalkeeper Donovan Ricketts.
The draw keeps RSL three points clear of third-place Portland, while the Colorado Rapids are two back of Salt Lake in second place.
Portland's Diego Valeri set up the opening goal and scored another from the penalty spot, but the loss is especially disappointing for the Timbers, who could have joined RSL in first place with two games in hand.
After Rodney Wallace opened the scoring in the 24th for the hosts, Nat Borchers scored on a rebound to level the match before Javier Morales drew a questionable penalty kick, and then converted to put Salt Lake up 2-1 at halftime.
Portland equalized in the 57th with a penalty kick of its own after Salt Lake's Tony Beltran was called for a handball. Valeri stepped to the spot and sent goalkeeper Jeff Attinella the wrong way, leaving everything to play for.
RSL's Yordany Alvarez was shown a straight red card for a poor challenge on Diego Chara, and Alhassan's goal four minutes from time looked like it would be decisive.
But Grossman came off the bench to rescue Salt Lake and keep his team atop the Western Conference.