On the winning play, the 5-foot-2 Opara got a head on Graham Zusi's corner kick, bouncing the ball into the net in the dying seconds of the match.
Soony Saad scored in the 67th minute to erase a 1-0 deficit as SKC (10-5-6) emerged with a victory in a battle between the MSL's two conference leaders.
Robbie Findley broke a scoreless tie in the 56th for Salt Lake (11-6-4).
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