The game remained scoreless after 20 minutes of play. The Canadiens led 10-6 in shots.
The Senators broke the stalemate 1:28 into the second period with a goal from Shane Pinto. Soon after, Drake Batherson doubled their lead on the power play.
The home side took advantage of another man-advantage when Brady Tkachuk made it 3-0.
After two periods, D.J. Smith's squad maintained their three-goal lead.
Near the halfway mark of the final stanza, Jake Evans chased down a puck in the Senators zone and fed a beautiful backhand pass to Kirby Dach, who buried it past goaltender Cam Talbot.
Then, Christian Dvorak cut into Ottawa's lead to make it 3-2. Nick Suzuki and Evgenii Dadonov earned assists.
Unfortunately, Martin St-Louis' contingent was unable to complete the comeback.
The Habs are back in action in less than 24 hours when they welcome the Anaheim Ducks at the Bell Centre at 7:00 p.m.