Canadiens assistant coach Perry Pearn was fired before the game. GM Pierre Gauthier told his players the news in the team's dressing room a few hours before the pregame warmup.
"It was a big shock to all the players. We didn't see it coming at all," said Pacioretty, who was a game-time decision because of an upper-body injury.
"When things are not going your way you've got to mix things up and it kind of sent a message to the players that they're willing to do what it takes to win hockey games.
"It's a decision that management made. None of the players were really involved in that but it showed us that no one's job is secure, and we've got to bear down at a time like this and do what we can to win."
Pacioretty assisted on Andrei Kostitsyn's goal 10:26 into the second and scored 2:12 later to make it 3-1. He added his second goal of the game in the third.
Yannick Weber scored a power-play goal late in the first period to tie it at 1. Michael Cammalleri also scored for the Canadiens, who got their first win in six games at the Bell Centre (1-3-2).
"We needed to get that one," Price said. "It was a tough stretch there, honestly. It was pretty tough mentally on everybody so we're just glad to have that over with and at least we have a chance to get right back into it (Thursday) night (in Boston). Hopefully we can continue what we did tonight."
The Canadiens, who are 2-5-2 overall, had not gone this deep into a season before getting their second win since 1941-42, when they got off to a 1-10-1 start.
"They have a lot of back pressure back through the middle," said Scott Hartnell, who assisted on Jagr's goal which opened the scoring midway through the first.
"When we turn pucks over it seems like their D are joining and there's at least three guys caught and they're coming 4 on 2. And we didn't do it just once or twice, we did it that whole second and third period."
The Canadiens failed to score on their first opportunity after Philadelphia was called for a penalty 58 seconds in.
Jagr soured the sold-out Bell Centre crowd's somber mood further when he put the Flyers up 1-0 at 10:43 on a goal sealed with his trademark salute.
Weber sent a jolt of energy through the building with 2.6 seconds left in the first when he drove a point shot inside the left post for his second goal and Montreal's fourth power-play goal of the season.
Kostitsyn got credit for putting the Canadiens up 2-1 midway through the second. Daniel Briere's clearing attempt went in off Kostitsyn's right skate, prompting a video review that upheld the goal.
Pacioretty, who left Monday night's 2-1 loss to Florida late in the second with an upper-body injury, made it a two-goal lead at 12:38 when a redirected puck left him a shot at an open right side for his third goal.
He made it 4-1 with his second goal of the game -- his fourth of the season -- 3:16 into the third. Cammalleri increased the lead to four with his third goal at 15:36.
Pronger is on bedrest and expected to miss two to three weeks after suffering an eye injury in Monday night's 4-2 win over Toronto.
Pronger, who does not wear a visor, was struck on the outside of his right eye by Maple Leafs center Mikhail Grabovski's stick blade.
Flyers C Sean Couturier played his ninth game and GM Paul Holmgren will now have to decide whether he will remain with the team or be returned to his junior team. Couturier, who has two goals and two assists, was selected eighth overall by Philadelphia in the June draft. ... Flyers coach Peter Laviolette used his timeout 4:29 into the second. ... Price, who is 100-80-26 overall, was rested for the first time this season Monday. He had failed in five straight attempts to get his milestone win following a 5-1 win in Winnipeg. ... The Canadiens went 1 for 5 on the power play.