DiPietro and Begin both fell to the ice after the Islanders goalie was hit on the right side of his mask by the Canadiens forward's right skate when he lunged forward to win a race to the puck just inside New York's blue line.
Begin grimaced in pain and had to be helped off the ice while DiPietro lay still on his back as he was being attended to by Islanders trainer Garrett Timms.
The goalie removed his mask and looked groggy as he was helped off the ice, passing backup Mike Dunham -- who replaced him 15:41 into the opening period -- in the hallway leading to the dressing room.
DiPietro, who entered with a 2.60 goals-against-average, a .918 save percentage and a 30-19-7 record, was making his 58th appearance of the season.
The Islanders led 1-0 on captain Alexei Yashin's first goal since he returned to New York's lineup Thursday after missing 14 games because of a knee injury.