"We've lost ourselves a little bit here," Flyers coach John Tortorella said. "I think we've lost confidence offensively, although I thought we generated some offense today. That's how the League works sometimes, you have some good weeks and you have some struggles. We're having some struggles now. We've just got to try to put our head down and see if we can solve some problems and get better."
Pastrnak scored the first of four Bruins goals in a 4:14 span in the first period, with a shot from the right face-off circle making it 1-0 at 14:09
"I was looking to give and go with 'Pav' (Pavel Zacha), but then I recognized I have a little bit more time," Pastrnak said. "I saw my [defenseman] and tried to go through his legs and definitely use the [defenseman] that was on me as a screen."
McAvoy put Boston ahead 2-0 at 15:46 when he pinched down and scored from the backdoor off a pass by Zacha.
Heinen made it 3-0 at 16:47 when he tipped a shot by Brandon Carlo.
Pastrnak finished the run with a goal from in front to make it 4-0 at 18:23.
"I actually thought the Flyers were significantly better than us the first 10 minutes of the game, and our big-time players made some big-time plays, including our goaltender, who was spectacular," Bruins coach Jim Montgomery said.
Van Riemsdyk, playing his first game back in Philadelphia since signing with the Bruins on July 1, scored to push the lead to 5-0 at 1:15 of the second period. Pastrnak got to a loose puck behind the Philadelphia net and found van Riemsdyk in front.
"He's a game-breaker, right?" Montgomery said of Pastrnak. "And he gives us an advantage that, in close games, we can win them."