Brayden Schenn scored, and Jordan Binnington made 34 saves for St. Louis (3-7-0).
"I think in the third period, we didn't come out with enough urgency," Blues coach Craig Berube said. "It seemed like we were in our end too much, and we gotta be better on the penalty kill and the power play. We had three power plays in the first period, didn't get a lot accomplished, and they scored two power-play goals. That's the game, so we gotta be better."
DeBrusk gave Boston a 1-0 lead at 13:34 of the first period, streaking through the slot and receiving a backhand pass from David Pastrnak on the power play. Marchand had the secondary assist.
"That's what they're looking for because it's a money play, and they still find ways to make plays," DeBrusk said. "On my goal, I knew that puck was coming through. I didn't know how, but I knew [Pastrnak] was going to try it, and it caught me off guard."
Schenn tied it 1-1 at 11:37 of the second period, completing a give-and-go with Jordan Kyrou at the doorstep.
"Effort's there. We showed up tonight," Schenn said. "We competed hard, that's a good team over there. You know, just got to find a way to score goals and get the results we want."