"That was so much fun," Kastelic said. "Probably the most memorable game of my career and super exciting to do it with the guys in that room. They're so supportive and it's just a fun atmosphere to be in."
Alex Formenton tied the NHL lead with his fifth shorthanded goal, and Anton Forsberg made 44 saves for Ottawa (31-41-7), which has won three straight.
"It was a long game, and wild," Senators coach D.J. Smith said. "There wasn't a ton of structure either way, but credit to our guys. … We found a way to win. We weren't as sharp as we've been, but there was a lot of emotion, and it was a fun game."
Rem Pitlick scored twice, and Carey Price made 20 saves for Montreal (20-48-11), which has lost eight in a row.
"It [stinks] to lose," Pitlick said. "I think that as a team, and as an athlete, there is that fire and frustration when you lose. Like, we're [ticked] off. But we're just going to keep working. There's nothing you can do other than trying to keep getting better and hopefully it bounces in your favor."