Alex Galchenyuk scored 3:40 into overtime, leading Montreal to a 3-2 victory over the Ottawa Senators on Friday night that gave the Canadiens a 2-0 lead in their first-round playoff series.
Max Pacioretty, back from a concussion, and P.K. Subban scored in regulation for the Canadiens, while David Desharnais picked up an assist on each.
Clarke MacArthur and Patrick Wiercioch scored for the Senators, and Mark Stone added two assists.
Pacioretty returned to the lineup for the Canadians after sitting out Game 1 with the head injury he suffered near the end of the regular season.
Carey Price stopped 29 shots for Montreal, while Ottawa's Andrew Hammond made 37 saves.
Game 3 is Sunday in Ottawa.