Newhook took a cross-ice pass from Alexandre Carrier, skated to the top of the left circle, and scored with a low wrist shot that beat the glove of Ukko-Pekka Luukkonen.
Phillip Danault and Zachary Bolduc also scored for the Canadiens, who are the No. 3 seed from the Atlantic Division. Jakub Dobes made 37 saves.
Montreal will face the Carolina Hurricanes, who are the No. 1 seed from the Metropolitan Division, in the Eastern Conference Final. Game 1 of that best-of-7 series will be in Raleigh, North Carolina, on Thursday (8 p.m. ET; TNT, HBO Max, truTV, SN, CBC, TVAS).
Rasmus Dahlin and Jordan Greenway scored for the Sabres, who were the No. 1 seed from the Atlantic. Luukkonen made 22 saves.
Danault gave Montreal a 1-0 lead at 4:30 of the first period when Kaiden Guhle’s centering pass deflected off his right skate and past the left pad of Luukkonen. The play started after Josh Anderson won a race for the puck with Bowen Byram below Buffalo's goal line.
Bolduc scored on the power play to make it 2-0 at 14:29. Nick Suzuki sent a no-look backhand feed from the left corner to Bolduc, who roofed a one-timer over Luukkonen's glove and under the crossbar from the right circle.
Greenway cut it to 2-1 at 13:19 of the second period. Mattias Samuelsson’s shot from the high slot deflected in off his left leg as he was screening Dobes in front.
Dahlin tied it 2-2 at 6:27 of the third period. Owen Power skated down the slot and sent a short feed to his fellow defenseman, who one-timed it short side over Dobes' blocker from low in the left circle.
