Collin's game-winning kick came after RSL's Lovel Palmer hit the crossbar on the preceding attempt. It handed SKC a 7-6 decision in the shootout.
Salt Lake had missed its first two shootout tries, but then came roaring back to force a sudden-death situation in the third-ever MLS Cup Final shootout.
The tiebreaker was necessary after the two team ended regulation in a 1-1 tie.
Collin, however, notched the equalizer in the 76th minute, heading a Graham Zusi corner kick past RSL's Nick Rimando.
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