Anders Lee scored for the Islanders (16-10-3), who have lost three straight games. Jaroslav Halak made 30 saves.
"Power-play-wise we need to click a little better," Islanders defenseman Calvin de Haan said. "I thought it was pretty sloppy for the most part the entire night. So sharpening that up, it helps give guys confidence. It's one game ... [the Bruins] did a good job. It's on us to be that much better and find ways to get wins."
Marchand gave the Bruins the 1-0 lead with a power-play goal at 10:51 of the second period. After Krug carried the puck up the ice, he hit Marchand in stride at the New York blue line. Marchand beat Halak with a wrist shot from the left dot.
DeBrusk extended the lead to 2-0 with an acrobatic move at 6:45 of the third period. The rookie received a pass from Krug at the bottom of the left circle, skated to the high slot and spun around before beating Halak high to the glove side with a wrist shot.
"I just wanted to get the puck on net," said DeBrusk, who scored his sixth goal of the season. "I was kind of trying to obviously generate maybe a rebound. It was kind of a weird play, I didn't really know where the net was. I kind of had an idea but I just turned and just shot as hard as I could and it went in. So it was nice to see that."