"Since we clinched, our intensity and concentration level, our attention to detail and our work ethic, have fallen a lot," Therrien said after the loss that helped the struggling Flyers end a four-game losing streak. "You see the results.
"It's a game of pride. You have to come to the rink ready to play. That's what we were not doing the last two games. There's no work ethic there right now. It's disappointing."
Philadelphia is in 12th place in the Eastern Conference, four places and seven points behind the New York Rangers and the postseason cutoff. The Flyers have six games remaining, starting with a home matchup with the Rangers on Tuesday.
The Flyers outshot Montreal 33-28 in a sloppy game that had the 21,273 at the Bell Centre booing the Canadiens.
Canadiens goalie Carey Price was pulled for a second game in a row in favor of Peter Budaj. Price left at the end of the second period after allowing six goals on 29 shots.
"Carey Price obviously didn't have his best night," said Hartnell, whose team scored only three goals in its previous four games. "We had traffic in front, we were making plays, we were moving our feet in the offensive zone.
"We weren't standing still with the puck. It's lot more fun to play games like that instead of 0-0."
The Canadiens are in danger of losing three in a row for the first time this season when they play at first-place Pittsburgh on Wednesday.
"We always bounced back all season," said defenseman Francis Bouillon, who was minus-3 on Monday. "We've got a lot of character in this room.
"It would be nice to win a few games. We're not focusing on the playoffs now, but it's important for us to play some good hockey before the playoffs."
They could be without Ryan White for a while. White was ejected in the first period for a direct hit to the head of defenseman Kent Huskins, when the Canadiens were trailing 2-0 just 6:11 in. The Flyers said Huskins had a concussion, and he didn't return to the game.
White launched himself at Huskins but missed his body and caught him on the jaw. Already in trouble with Therrien earlier in the season for taking ill-timed penalties, White's future with Montreal now looks in doubt.
Price, pulled in Toronto on Saturday after allowing three goals on four shots, gave up two goals on five Philadelphia shots before settling down. The Flyers outshot Montreal 17-8 in the first period.
"It isn't easy to play every game at the same level," Canadiens defenseman Andrei Markov said. "Other players can make a mistake, and your partner can cover you. We support him."
Simmonds broke down right wing and fired a shot that was stopped by Price, but the rebound hit rookie Montreal defenseman Nathan Beaulieu and went in at 2:45.
Gustafsson's wrist shot from the point went through several bodies in front and trickled between Price's pads at 5:49.
Consecutive cross-checking calls on the Flyers' Oliver Lauridsen allowed the Canadiens to tie it as Pacioretty tipped in Tomas Plekanec's pass in the slot at 19:02. Gallagher scored from in front 38 seconds into the second.
Only 24 seconds later, Josh Gorges overskated a puck behind his net, and Giroux pounced and fed Voracek as the Flyers took a 3-2 lead. Voracek's 18th goal tied a career high set last season.
Hartnell scored from the slot on a power play at 7:30, but Galchenyuk fought off a check to score at 9:11. Giroux put one in off Markov's stick at 10:46 for a 5-3 Philadelphia lead.
Hartnell snapped a shot past Budaj from the top of the left circle 12:45 into the third.
A moment of silence was held for victims of the Boston Marathon bombing. ... Montreal rested banged-up forward Brandon Prust. White took his place in the lineup.
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MONTREAL, CANADA - APRIL 15: Gabriel Dumont #37 of the Montreal Canadiens warms up before the NHL game against the...