Wideman cut it to 2-1 at 9:33 of the second period when he was left uncovered at the right side of the net. It was his first goal since Oct. 13, 2018, when he scored twice for the Ottawa Senators against the Los Angeles Kings. Wideman played in the American Hockey League in 2019-20 and in the KHL last season.
Olofsson scored on the power play from the right circle at 17:05 to put Buffalo ahead 3-1, and Anders Bjork pushed it to 4-1 at 19:04, pouncing on the rebound at the side of the net after Girgensons' shot hit Canadiens defenseman Ben Chiarot.
"In the first period, we were bad in every aspect, including the way we were competing," Canadiens coach Dominique Ducharme said. "We didn't play to our team identity, that's for sure. We had a better start to the second, and then the penalties we took hurt us."
Tage Thompson extended the lead to 5-1 with another power-play goal at 4:29 of the third period. Olofsson's initial shot from the right circle was blocked and bounced out to Thompson, who shot top shelf from the left circle.
"You could see the emotion on the bench, on the ice, in the crowd, everywhere tonight," Okposo said. "It was a full-building effort tonight from us and we definitely drew off the fans, drew some energy from them, and it was great to have them back in the building. It makes a huge difference. But yeah, I thought we rolled tonight. I thought special teams were really good. A little bit out of rhythm of the game there in the second, or first and second, but 5-on-5 I thought we played a full team game."
NOTES: Sabres center Casey Mittelstadt left in the second period with an upper-body injury. Coach Don Granato did not have an update after the game. … The win tied Buffalo's largest margin of victory in a season opener in its history, with the most recent occurrence happening against the New York Islanders on Oct. 10, 2002 (also 5-1). … The Canadiens are 0-2-0 to start the season for the first time since 2000-01.