Kronwall's deciding goal was scored 2:16 into the third period when he fired a slap shot through a crowd and past Montreal goalie Jaroslav Halak.
Eric Nystrom, who scored twice for the Flames, thought he had his first career hat trick after being credited with Kronwall's goal. The sold-out crowd sent hats sailing onto the ice after Nystrom was announced as the goal scorer.
Montreal carried the play most of the third period, threatening several times to tie the game, but Miikka Kiprusoff stopped all 15 shots he faced in that final 20 minutes.