Ferrari's goal capped a comeback for Montreal, which had trailed 2-1 in the second half.
Marco Di Vaio scored the equalizer in the 80th minute when he got past a pair of defenders and put a shot into the net off the left post.
Then with time running out, Montreal had a corner kick and Ferrari -- who had scored an own-goal in the 7th minute -- got control of a loose ball in the box, blasting it past Nick Rimondo just before the final whistle.
Felipe Martins also scored for the Impact (6-2-2).
Kyle Beckerman found the net for Salt Lake (5-5-2).