Hossa's goal late in the second period gave the Blackhawks their first lead at 4-3. He added an empty-net goal with 16 seconds left that turned out to be the game-winner after Toronto's Mike Brown
scored with four seconds remaining.
Patrick Kane had a goal and an assist for the Blackhawks, and rookies Marcus Kruger and Andrew Shaw also scored for Chicago, which won for only the fifth time in its last 17 contests.
The Leafs were unable to hold on to a 3-1 lead they built late in the first period for embattled coach Ron Wilson.
Toronto, which has just one win in its last 11 games, came out strong a night after fans at Air Canada Centre showered the team with chants of ``Fire Wilson!'' in the third period of a 5-3 loss to Florida. Tyler Bozak
, Joffrey Lupul
and Clarke MacArthur
scored in the first period for the slumping Maple Leafs.
The Blackhawks came in having lost three in a row.
Chicago's Corey Crawford started in goal, but was replaced by Ray Emery to start the second after allowing three goals on 10 shots. Emery was sharp and stopped 23-of-24 shots.
Toronto's Jonas Gustavsson
was shaky at times, but finished with 30 saves.
Blackhawks captain and leading goal scorer Jonathan Toews missed his fifth game with an upper-body injury, believed to be a concussion. Defenceman Niklas Hjalmarsson sat out his third straight, and 10th in his last 11, with concussion symptoms.
Defenceman Johnny Oduya, acquired by Chicago from Winnipeg just before Monday's trade deadline, played his first game with Chicago.
The Blackhawks went 0-for-2 on the power-play and have scored just one goal in their last 41 chances.
The Maple Leafs led 3-2 after a first period that mirrored the recent play and records of the two teams.
Bozak opened the scoring 59 seconds in from the side of the net with a soft goal when he slipped a backhand shot under Crawford's pads.
Shaw tied it 1-1 with 8:59 left in the first when he drove from the left corner into the slot and beat Gustavsson between the pads. Shaw connected in his first game after being recalled from Rockford of the AHL for the second time this season.
Lupul's power-play tip in just 28 seconds later, set up by Phil Kessel
's pinpoint feed, restored the Maple Leafs' lead at 2-1.
MacArthur made it 3-1 with 3:07 left in the first. After Mikhail Grabovski
's shot struck the skate of Blackhawks defenceman Brent Seabrook, MacArthur shovelled in the loose puck before Seabrook could find it.
Kruger's deflection of Nick Leddy's shot from the point cut it to 3-2 with 30 seconds remaining in the period.
Chicago led 4-3 after two periods thanks to goals by Kane and Hossa on strong efforts.
Kane tied it 3-3 at 8:33 of the second. He pounced on a rebound of Andrew Brunette's shot, plowed into traffic and flipped in a high shot from a sharp angle to Gustavsson's left.
Hossa gave Chicago its first lead at 4-3 just over four minutes later. After driving down the slot and past two Toronto defenders, Hossa fired a shot just inside the left post.
Emery made a tough kick save on Toronto rookie Matt Frattin
with 4:30 left in the third to preserve the lead.
Blackhawks LW Brandon Bollig appeared in his first NHL game following his recall from Rockford on Tuesday. He fought Toronto's Luke Schenn
. ... Chicago D Steve Montador missed his 11th game with an undisclosed upper-body injury. ... Toronto C Matthew Lombardi was a healthy scratch for the first time this season. He has just one goal and two assists in his last 15 games and is a team-worst minus-13. ... The game was the only one this season between Chicago and Toronto, both Original Six franchises. The teams have not played more than once in season since 2001-02 and over the last nine seasons have met only seven times.