First, Niemi made a career-high 52 stops as the Canadiens extended their win streak to three games with a 5-1 victory over the Florida Panthers.
Niemi finished one save shy of the Canadiens' franchise record for saves in a game by a goaltender.
With seconds ticking off the clock in the third period, the Bell Centre fans chanted Niemi's name after every big save.
"I don't know if I've ever heard that before," Niemi said. "So it's pretty overwhelming. It's great after all my ups and downs to have a couple of good games and be able to do that.
"It's great. I don't know what to say."
The Panthers fired 84 pucks at Niemi's goal, with 53 hitting the target and only one making it past the backup goalie. The franchise record is 53 saves held by Carey Price (Nov. 14, 2009) and Wayne Thomas (Mar. 10, 1974).
Florida lost its seventh game in a row, extending the team's longest skid of the season. Their last victory was on Dec. 31, against the Detroit Red Wings.
The 35-year-old Niemi, who has won his last three starts, made 21 saves in the third period alone to improve to 8-4-1 on the season. His previous personal save record was 48, set on March 3, 2017, in a 2-1 loss to the Bruins.
"He played unbelievable tonight. It was crazy," Jordie Benn said. "Nemo stole the game. They had some really close-call looks right in tight. Watching him in net tonight, the guys were going nuts on the bench. It was good to see."
Niemi set the tone with a solid glove save on rookie Juho Lamikko midway through the first period.
"He's the guy who's literally the hardest working guy in practice," said Max Domi, who snapped a 17-game goalless drought. "He works on his game on a daily basis. It's a very well-deserved performance by him. He's been in this league so long for a reason. He showed that tonight."
Mike Hoffman was the only Panthers player to beat Niemi. He scored a highlight-reel, one-handed goal on a breakaway at 14:11 of the first period, following a bad giveaway by Canadiens center Michael Chaput.
Claude Julien's team had not scored on their previous 27 power-play opportunities at Bell Centre, dating to Dec. 1.
Phillip Danault gave the Canadiens a 2-1 lead at 10:44 of the second, a no-look backhand shot after Weber's shot bounced off the end boards behind Reimer.
Domi scored his first goal since Dec. 9 when he beat an out-of-position Reimer at 16:53 with a wrist shot from the slot.
Jesperi Kotkaniemi added another for Montreal with 5:38 left in the third period before Gallagher scored into the empty net with 1:36 remaining in the encounter.
"Tough road trip obviously physically and mentally," said Panthers coach Bob Boughner. "We asked the guys to come out tonight with our best effort and get rewarded. We did everything except putting the puck in the back of the net. You have to give Niemi a ton of credit."
The Canadiens were playing in the second half of back-to-back games after a 3-2 overtime victory in Boston on Monday.
Roberto Luongo was expected to start between the pipes for Florida but Reimer got the nod instead in a game-time decision. Reimer stopped 23 shots in defeat.
The Panthers outshot the Canadiens 53-28. . Jordie Benn earned his 100th NHL point in his 439th game. . Defenseman Karl Alzner was sent down to the AHL's Laval Rocket.
Panthers: Home against Toronto on Friday.
Canadiens: At Columbus on Friday.
More AP NHL: https://apnews.com/tag/NHL and https://twitter.com/AP-Sports