Toronto has won six of seven and is playing its best hockey of the season. Four of those victories have come after regulation time.
Mitchell and Nikolai Kulemin beat Jaroslav Halak in the shootout. Jonas Gustavsson stopped two of Montreal's three attempts. He sealed the win with a save on Brian Gionta.
Tyler Bozak and Phil Kessel scored in regulation for the Maple Leafs, who are 29th in the overall standings of the 30 NHL clubs.
Gionta had both goals for Montreal.
Gustavsson made 25 saves and extended his winning streak to five games. Halak stopped 31 shots.
The Canadiens squandered a chance to leapfrog Ottawa and Philadelphia in the Eastern Conference standings. They entered with a six-game winning streak and would have moved into fifth place with another victory.
There was very little intensity in a game between the old rivals.
Bozak opened the scoring by netting his seventh of the season at 16:05 of the first period. The rookie had a wide-open net after a shot from Kulemin hit the post and bounced out to him.
Montreal tied it before the period was over. Gionta raced up the right wing and beat Gustavsson with a backhander the Leafs goalie would probably like to have back.
Kessel put the Leafs back in front with a wicked shot from the top of the circle that beat Halak to the glove side at 18:15 of the second. Kessel has six goals in six games and is closing in on the 30-goal mark for the second straight season. He has 28 goals.
Gionta was standing in the high slot and tipped Scott Gomez's shot behind Gustavsson at 13:54 of the third.
That set the stage for overtime — the fourth time in five meetings this season the teams have been stretched past regulation.
NOTES: Kulemin had two assists. ... Ben Maxwell and Paul Mara were scratched for Montreal. ... Luca Caputi and Jeff Finger sat out for the Leafs. ... Toronto forward Christian Hanson played in his 21st game of the season and has yet to score a goal.