Making his ninth start for the Canadiens, Halak allowed two weak goals in the first seven minutes of the game. Coach Guy Carbonneau pulled him at the start of the second period when the Thrashers scored a third goal only a few minutes into the period.
Max Pacioretty and Patrice Brisebois scored the only goals for the Canadiens, but it was too little too late.
Zach Bogosian sealed the deal for the Thrashers with a goal that gave them the 4-2 victory.
Before tonight's game the Habs had won two in a row and were 11-2-1 in their last 14 games.
The Habs are in New Jersey to face the Devils tomorrow night. Carey Price will get the start in goal for Montreal.