Rasmus Ristolainen had a goal and an assist, and Linus Ullmark made 19 saves for the Sabres (17-16-7), who have lost three in a row and are 1-5-1 in their past seven games.
"Yeah, it's definitely painful at this moment because the effort was there right through and we were building an excellent game," Sabres coach Ralph Krueger said. "It took a different course in the third. I think everybody can make judgment of where that happened, and I was pleased with the reaction of that, guys came back at it and they never gave up on it."
With Sabres forward Johan Larsson called for a double-minor at 1:23 of the third period for tripping DeBrusk and hooking Brad Marchand, DeBrusk gave the Bruins a 2-1 lead at 2:37 with a redirect of a pass by Steven Kampfer, who had his first two assists of the season.
"Yeah, so I saw him coming around the net," Kampfer said. "[Pastrnak] made a great play up the seam there when I was at the point, and then I saw Jake kind of get lost and turned around, he was standing right there, so it was a pretty quick play, but I was glad he was there."
DeBrusk made it 3-1 at 2:55 with a shot from the left corner that went past Ullmark on the short side.
Curtis Lazar cut the lead to 3-2 at 5:08 on a rebound of a Ristolainen shot.
