Matt Moulson scored for Buffalo and Ryan Miller made 28 saves as the Sabres lost their fifth consecutive game in regulation.
The Montreal power play continues to thrive under defenseman Andrei Markov. He had two of his three assists with the man advantage as the Canadiens converted on 2 of 4 opportunities.
"He's such a smart player," Therrien said. "He sees the ice well. He's got experience and his conditioning is great because he's put a lot of effort at it."
The defenseman said the power play's success is coming from good team movement.
"The power play's about a unit of five," Markov said. "Your five guys on the ice have to work together and we try to move the puck and put the puck in the net."
Montreal scored first at 17:21 of the first when Lars Eller slid a drop pass to Markov, who caught Miller out of the net. Markov's shot deflected off Galchenyuk and into the goal.
It marked Markov's fourth straight game with a point.
The Sabres briefly lost Moulson when the left wing was hit into the boards by P.K. Subban midway through the second period. Subban was not penalized, and the Canadiens earned a power play when Foligno was unsuccessful in an attempt to fight Subban.
On the ensuing power play, Subban fired a slap shot from the left point that Desharnais deflected past Miller to put the Canadiens up 2-0 at 13:44 of the second.
The goal was Desharnais' second in three games after failing to score in his first 20 games of the season. He became the 12th Canadiens player to score a power-play goal this season.
"In the last two weeks he's played well," Therrien said. He's competing well. He's working hard at both sides of the ice."
Buffalo got even with Subban late in the second period when Drew Stafford put the defenseman on the ice before finding Moulson, who beat Price to make it 2-1 at 17:30 of the second.
Brendan Gallagher restored the Canadiens' two-goal lead at 18:16 of the third, when his one-time shot beat Miller for a power-play goal.
The Sabres are 1-5 under interim head coach Ted Nolan, who says he's seeing signs from a struggling team that's won just twice in 14 home games.
"The one thing we asked our team to do is compete, and we competed," Nolan said. "When things are difficult, it's easy to point fingers, but this group is really starting to pay attention. We're making strides in the right direction."
The Canadiens' third-best road penalty killing unit did the job, holding off the Sabres on a four-minute power play in the first period.
The game was Buffalo's fifth straight allowing at least one power-play goal.
Douglas Murray left the ice for stitches after a lengthy third-period fight with Sabres enforcer John Scott opened a large cut above his left eye.
The Sabres were awarded RW Matt D'Agostini off waivers from Pittsburgh earlier Wednesday. ... Canadiens RW Rene Bourque missed his fourth game with a lower body injury ... Montreal extended assistant general manager Rick Dudley's contract before the game after Buffalo had requested permission to interview him for their vacant general manager position.
Copyright by STATS LLC and The Associated Press
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