Mark Kastelic (2), Austin Watson, Parker Kelly, Josh Norris and Alex Formenton scored for the Sens (31-41-7) as Anton Forsberg made 44 saves. Montreal's (20-48-11) Carey Price stopped 20 shots as Rem Pitlick (2), Cole Caufield and Joel Edmundson had goals.
"Probably the most memorable game of my career," Kastelic, who scored his first two NHL goals, said. "It's exciting to be able to do that with the guys in that room, who are so supportive, and it's such a fun atmosphere to be in."
Ottawa jumped out to a 1-0 lead and it came on Kastelic's first NHL goal at 2:33 as he threw the puck goalwards from the right boards and it squeaked in through Price. The 23-year-old had no time to celebrate however as he took a hit from Michael Pezzetta as he shot and wound up dropping the gloves with the Habs forward.
"I have not done that before," Kastelic said with a smile. "That's a first. In my defence, I did not know that I had scored so it was kind of a funny situation."
Montreal tied the game at 15:57 on Pitlick's 14th as he was all alone inside the left dashes to make it 1-1.
After Watson's tip 44 seconds into the second gave Ottawa a 2-1 lead, the Sens would then explode for three goals in a span of 1:07, the second fastest three goals in franchise history.
Kelly's seventh of the year came at 6:45 before Norris grabbed his 34th at 7:15 as Brady Tkachuk expertly banked the puck in off his linemates skate.
Kastelic's second of the evening came at 7:50 as he deked quickly in front of Price before he lifted the puck high for his first career multi-goal NHL game.
"The second one definitely felt like more of a real goal to actually see [the puck] go in and have that moment was pretty special," he said.
Montreal cut into Ottawa's lead on goals from Caufield and Edmundson but Formenton's fifth short-handed goal of the season at 18:05 gave the Sens a 6-3 lead after 40 minutes.
Pitlick's second of the night came at 8:19 of the third as he cut the Sens lead to two goals but Forsberg turned aside 15 shots in the final frame to preserve the win.
"Credit to our guys ... we found a way to win," Sens head coach D.J. Smith said.
Senators defenceman Thomas Chabot returned to the lineup tonight after an 18-game absence with a fractured hand. The star blueliner played 20:21 and tallied two shots on goal.
"It was fun to get back out there with the guys," Chabot said. "To get the win in front of our fans was awesome."
Ottawa's three-game homestand continues Tuesday when they host New Jersey. Puck drop is 7 p.m.
