The Blackhawks, who began the night tied with Anaheim for seventh place in the Western Conference, halted a two-game skid.
St. Louis tied it on a wrist shot by Chris Stewart with 10:16 to play in regulation.
Corey Crawford, who was appearing in his 25th straight game for the Blackhawks, made 21 saves to get the win. Ty Conklin played in his 200th NHL game for the Blues and took the loss while stopping 35 shots.
The goal by Hossa that started the Chicago rally bounced off a skate and just slipped over the goal line. It took the officials 8 minutes of reviewing time to decide that Hossa did not intentionally kick the puck into the net.