Soares' tally off a Chris Tierney corner kick gave the Revolution (9-17-8) its first victory in Canada in nine all-time games.
The Revs' tally came shortly after Davy Arnaud nearly won it for Montreal (12-16-6), His try was cleared off the New England goal line.
Although they missed the MLS playoffs, the Impact will play again next month, taking on Bologna F.C. Nov. 8 in Italy.
2014 amfAR Inspiration Gala [PHOTOS]
Julius Randle breaks leg during NBA debut