Rask, the winningest goalie in franchise history, made his season debut after recovering from surgery last summer to repair a torn labrum. Rask was solid in net and got plenty of help from his teammates, who held Philadelphia to 27 shots as the Bruins won their fourth straight and seventh in eight games.
Boston fans greeted Rask with a rousing "Tuuuuuuuk!" when he was the last of the Bruins introduced before the national anthem. But he was mostly idle early as the Flyers didn't get a shot on goal for the first nine minutes.
By then the Bruins were already up 2-0 on goals by Pastrnak, who completed his 11th career hat trick with a power-play goal late in the second period after Philadelphia had scored twice.
Rask didn't face a shot until a harmless wrister from the blue line from Ivan Provorov at 9:19 of the first period. Rask faced just six shots in the first, none of which were particularly challenging as the Bruins controlled the play and spent most of the period in the Philadelphia end.
Hart had a much busier night, stopping Pastrnak from in close several times after he scored 1:51 into the game and again at 5:27 of the first.
Boston went on a 5-on-3 power play late in the second and this time there was no stopping Pastrnak, who one-timed a slap shot from the top of the circle past Hart, who had lost his stick a few moments earlier. Pastrnak's 16th goal of the season put the Bruins up 3-2 and started a flurry of hats coming down from the stands for the second night in a row. Brad Marchand, who assisted on Pastrnak's second goal, had a hat trick Wednesday night in a 5-1 win over Montreal.
Atkinson pulled Philadelphia to 2-1 on a power-play goal 8:02 into the second with a tip of a shot by Provorov from the blue line.
Philadelphia tied it 2-all with five minutes left in the second when Farabee's pass to Atkinson bounced off his skate right back to Farabee, who had Rask out of position and an empty net in which to deposit the tying goal.
Philadelphia had 51 seconds of a 5-on-3 power play after a delay of game penalty on Brandon Carlo and a charging call against Charlie Coyle. The only shot Philadelphia got on net was a slow bouncer that Rask scooped up despite a tip in front by James van Riemsdyk.
The Flyers pulled Hart with more than three minutes left in the third but were unable to get another equalizer.
NOTES: Rask hadn't played since June 9, when the Bruins were eliminated by the Islanders in the second round of the playoffs. ... Philadelphia's scheduled home game against Carolina on Tuesday was postponed because of COVID-19 issues with the Flyers. The extra couple of days between games allowed them to get a few more key players back from COVID-19 protocols and injury. Philadelphia captain Claude Giroux, Provorov, D Travis Sanheim and RW Travis Konecny all returned.
Defenceman Tyler Lewington, recalled from Providence of the AHL on an emergency basis Wednesday, jumped right into the game's first scrum after a hard hit in front of the penalty box late in the first period. Lewington was also involved in the game's first full-fledged fight after being challenged by Philadelphia's Zack MacEwen. The two exchanged blows in the Boston zone early in the second period in a bout reminiscent of the Broad Street Bullies and Big Bad Bruins of the 1970s.
Boston defencemen Derek Forbort and Connor Clifton were in COVID-19 protocol.
Flyers: Host the New York Rangers on Saturday.
Bruins: Host the Western Conference-leading Nashville Predators on Saturday afternoon.