Boston was 2-for-6 on the power play. Washington went 0-for-5.
"I think we had some poor execution on a few plays, and then were forced to take penalties when they were getting great opportunities, and they capitalized," Capitals coach Todd Reirden said. "So far too many penalties, obviously, and … if I had to point to one negative from 39 games into it, that would be it. They got a good power play and they were able to convert."
Jake DeBrusk scored a power-play goal at 5:37 of the first period to give the Bruins a 1-0 lead before Marchand extended it to 2-0 at 13:29. It was Marchand's 19th goal of the season, but his first in 13 games.
"Yeah, I mean it's just kind of been one of those stretches where the puck hasn't been bouncing the right way," Marchand said. "It was just a matter of time. I knew it was going to go in eventually, I wasn't too concerned about it, but it's nice when it does."
Anders Bjork made it 3-0 at 13:56, and Bergeron scored a 5-on-3 goal at 18:57 to extend the lead to 4-0.
"Obviously, we gave [Holtby] no chance. We left him alone out there in the first 10-to-12 minutes, take penalties, make bad plays," Capitals captain Alex Ovechkin said.