Dale Weise scored the tying goal late in the third period and then won it 8:47 into overtime, leading the Montreal Canadiens to a 2-1 victory Sunday night in their first-round playoff series.
Montreal has a chance to complete a four-game sweep Wednesday, with Game 4 in Ottawa.
Weise sent the game to overtime with his goal with 5:47 remaining in the third. Torrey Mitchell assisted on both goals, and Carey Price made 33 saves.
Clarke MacArthur opened the scoring for the Senators at 11:28 of the first period. Craig Anderson, making his first start of the playoffs, made 47 saves in the loss.
Montreal dominated at times in the second and third periods, outshooting Ottawa 31-15 through the final 40 minutes of regulation.