Montreal moved two points ahead of Philadelphia and Boston in the tight Eastern Conference playoff race. The Canadiens had dropped five of their previous six.
"If we get into the playoffs, it's a huge win. But if not, it's just a regular win," Halak said following his fourth shutout of the season. "We'll see how important a win it was in about a week from now."
Montreal has four games remaining, as does Philadelphia. The Flyers lost for the second straight night and have just one win in eight games (1-6-1). They are only two points above the postseason cutoff.
"We need to play that way, and [if we do], yes, I believe we'll get in," Flyers coach Peter Laviolette said.
Plekanec gave Montreal the lead it protected all night when he took a blind centering pass from Andrei Kostitsyn and beat Brian Boucher 9:25 into the game for his 24th goal.
"It was a playoff game, no doubt," said forward Brian Gionta, who led the Canadiens with four shots. "Each game is like this now."
Halak allowed five goals on 17 shots against the Flyers on Feb. 13, but was much stronger in the rematch. His best sequence came late in the second period when he made consecutive saves on James van Riemsdyk and Mike Richards. Just seconds later, van Riemsdyk skated in on a semi-breakaway and was denied again.
"He definitely made some key saves," Montreal coach Jacques Martin said. "He kept us in the game."
Halak benefited from a fortunate bounce with 7 minutes left when a wrister by van Riemsdyk caromed off his shoulder and trickled just past the right post.
"We had luck on our side, but I'll take it," Halak said.
Philadelphia also had a goal disallowed with 15:38 remaining because van Riemsdyk used a high stick to chop a floating puck into the net. The goal was immediately waved off on the ice, and the call was upheld after a video review.
Boucher finished with 22 saves for the Flyers, who will return to the ice Sunday against the surging Detroit Red Wings.
"We have to play this exact same way the next four games," Flyers defenseman Chris Pronger said. "Tonight was the blueprint. We've got to get it done."
Flyers C Jeff Carter (foot) is scheduled to have an MRI on Wednesday. He is expected to return in time for the playoffs. ... The best-case scenario for injured Flyers G Michael Leighton is "at least three weeks," general manager Paul Holmgren said. ... Canadiens RW Sergei Kostitsyn missed the game because of a lower-body injury. ... Pronger played in his 1,100th NHL game.
Copyright by STATS LLC and The Associated Press
Arena: Wells Fargo Center Location: Philadelphia, Pennsylvania
Referees: Dennis LaRue, Brad Meier Linesmen: Derek Nansen, Andy McElman
Attendance: 19,801 (101.5% full)
Team Stat Comparison
Power Play Goals
Power Play Opportunities
Shots on Goal
Tomas Plekanec (24)
Assists: Andrei Kostitsyn, Marc-Andre Bergeron