Calgary had a backup goaltender in net, and Matthew Tkachuk got the night off because of a suspension.
No big deal for Sean Monahan and the Flames.
Monahan scored his second goal of the game 1:14 into overtime, lifting Calgary to a 3-2 victory over the Montreal Canadiens on Thursday.
Monahan finished a 2-on-1 break by taking a feed from Johnny Gaudreau and beating Carey Price from the slot for his 17th goal of the season.
Never miss a local story.
Garnet Hathaway also scored for Calgary (15-12-2), which was coming off a shootout loss in Toronto on Wednesday night. David Rittich made 35 saves in his second career start.
Tkachuk served a one-game suspension for spearing Toronto's Matt Martin. It was the second suspension this season for the skilled but sometimes undisciplined 19-year-old forward.
"We'll be happy to have Chucky back next game and we'll build on it from there," Monahan said.
Daniel Carr and Phillip Danault scored for Montreal (13-13-4). Price stopped 34 shots.
"We did a lot of good things but the team over there was resilient," Price said. "Their goaltender played well for them and they found a way to win."
The Flames trailed 2-1 heading into the third period, but Hathaway tied it at 7:49 on a goal that needed two video reviews. The officials first ruled goaltender interference when the puck went in with Hathaway and two linemates jamming at the puck in the crease.
Flames coach Glen Gulutzan challenged the ruling, which was then overturned.
"Janko (Mark Jankowski), Benny (Sam Bennett) and I were buzzing," said Hathaway, who got his first goal of the season. "Benny made a nice play behind the net to bring it out in front and we were all jamming at it.
"That was a big goal for our line."
Each team scored from the side of the net in the first period. Monahan's first shot hit the side, but he picked up the rebound, spun around and sneaked the puck inside the near post at 6:31. Carr backhanded a shot off Rittich's back and in from close range at 8:36.
It was the sixth point in four games for Carr since he was promoted from the minors last week.
Montreal captain Max Pacioretty broke down the right side and backhanded a pass in front that Danault tipped over Rittich's glove at 10:10 of the second period.
"It wasn't a bad game, but little details cost us the game," Montreal coach Claude Julien said. "We need to win more battles along the boards and in front of the net.
"That's an area we need to improve quickly."
NOTES: With Tkachuk's suspension, F Freddie Hamilton moved into the Calgary lineup. ... Calgary F Curtis Lazar played in his 200th career game. ... Flames F Jaromir Jagr sat out a second straight game with a lower-body injury. ... Montreal started Jakub Jerabek on defense, bumping Victor Mete. ... Montreal F Jonathan Drouin skated Thursday morning but still missed a fourth game, the last two with an illness.
Flames: Host Vancouver on Saturday night.
Canadiens: Host Edmonton on Saturday night.