Saku Koivu, who tied the game eight minutes into the third period, also had an assist, and Cristobal Huet stopped 29 shots, including 23 over the final 45 minutes in dousing the NHL's most potent offence. Huet's best save came with a minute left in overtime when he closed his pads in time to prevent Thomas Vanek's attempt to squeeze a shot through on a breakaway.
Jaroslav Spacek scored for the Sabres (18-3-2), who entered the game with a league-leading 101 goals, and were coming off two seven-goal games, including a 7-4 win over Toronto on Wednesday.
Souray's goal came on the transition and after Buffalo's Maxim Afinogenov had his shot blocked in the Montreal end. Alex Kovalev carried the puck up the right wing and fed a pass across to Souray, who beat Ryan Miller on the short side with a snap shot from the left circle.