Mike Reilly extended the lead to 4-1 at 19:00 when he scored into an open net after the rebound of a point shot bounced to him in the left circle.
The four goals were 5:31 apart.
"Tonight was a product of them just shooting everything," Okposo said. "They made it a point, especially in the first and third, to just throw everything at the net and crash. We just didn't do a good enough job clearing the second opportunities, and they were able to cash in on that. The best way to eliminate that is spending more time in the O-zone. We just didn't do it enough in the latter half of the first period and in the third, especially."
John Hayden was awarded a penalty shot for the Sabres at 9:22 of the second period when Bruins defenseman Derek Forbort tripped him, but Swayman made the save.
Taylor Hall made it 5-1 from the left circle on the power play at 15:26.
"We've got to keep pushing and pushing ahead," Granato said. "It's unfortunate, but at the same time, we have to fight through and compete. If it's going to change, it's going to be those core [things], competitiveness. Obviously, we can look at the film and tweak … small details that we can look at. I looked at a few just after the game that need to be better. That will be our focus, absolutely."
NOTES: Boston defenseman Charlie McAvoy left the game at 13:46 of the third period after being hit into the boards by Buffalo forward Zemgus Girgensons. Girgensons was assessed a five-minute major for boarding and a game misconduct. "He got some stitches," Cassidy said. "He was up moving around, so he's good. … He'll have a gash over his eye." … The Bruins are 13-1-0 in their past 14 games against the Sabres dating to Dec. 29, 2018. … Hayden had three shots on goal and four hits in his 200th NHL game.