After 40 minutes, the game was tied at one apiece. The Habs continued to lead in shots on goal with 23 to the Flyers' 19.
In the third period, Frost scored his second of the game to give Philadelphia a 2-1 lead with less than five minutes to go.
Owen Tippett notched an empty netter to double their tally.
Rafael Harvey-Pinard cut into their advantage, but the Canadiens couldn't tie the game to force extra time. Jake Evans and Jesse Ylonen earned assists.