Travis Sanheim had a goal and an assist, Scott Laughton and Kevin Hayes each had two assists, and Carter Hart made 29 saves for Philadelphia (9-12-5), which won for the second time in 14 games (2-9-3).
"I think we were a little more sharp against the [New Jersey] Devils, didn't quite get the outcome (in a 3-2 loss Saturday)," Sanheim said. "Tonight, not quite as sharp and yet find a way to win a hockey game. So, sometimes that's how the game works and we're happy to come out with [the] victory."
Alex Newhook scored two goals, and Alexandar Georgiev made 29 saves for Colorado (13-9-1), which played the final two periods without center Nathan MacKinnon after he sustained an upper-body injury.
MacKinnon, who had an assist on Newhook's first goal,
left with 8:13 remaining in the first period
. He played five shifts totaling 4:58 of ice time.
Avalanche coach Jared Bednar did not have an update on MacKinnon after the game.
"It's a guy that plays 25 [minutes] a night and in every situation, so you have to juggle everything," Bednar said. "Do the best you can. You've just got to keep grinding and find guys that contribute."
The Flyers took a 4-1 lead on Owen Tippett's power-play goal at 9:54 of the third period.
But the Avalanche made it a one-goal game after Mikko Rantanen scored at 17:47, and Newhook got his second goal of the game with Georgiev pulled for an extra attacker at 18:23.
"We have the skill, we have the drive, the determination," Newhook said. "You saw that last year in our playoff run and it's still deep within our team. We're never out until we're out. To get it within one and still have a chance to win after that kind of a game, we've just got to find a way."