The Maple Leafs built a 3-1 lead during the game's first 16:53, but could not score again until Mike Brown tallied in the final seconds of regulation to cut Toronto's final deficit to one.
Marcus Kruger began the Chicago comeback by tipping in a shot with 30 seconds left in the first period and Patrick Kane tied it on a backhander 8:33 into the second.
Hossa gave Chicago the lead with 7:54 to go in the middle period and then scored into an empty net with 16 seconds remaining for what turned out to be the game-winning goal.
Chicago ended a three-game slide that had pushed the Blackhawks within three points of falling out of a playoff position. Corey Crawford started in goal for Chicago, but was removed at the end of one period after giving up three goals on 10 shots.
Ray Emery finished up to get the win, making 23 saves. Jonas Gustavsson surrendered four goals on 34 shots for the Maple Leafs, who have suffered six straight losses.