The loss was Philadelphia's fifth straight and eighth in nine games.
Kastsitsyn tied the score at 13:40 and Cammalleri put Montreal ahead on a 2-and-1 break just under 9 minutes later. Marc-Andre Bergeron scored the final goal on a power play with 8:33 remaining in the third period.
Montreal goalie Carey Price ended up with 14 saves.
Danny Briere got Philadelphia's goal 7 1/2 minutes into the first period and Brian Boucher made 10 saves.