Pageau tied it 1-1 at 11:36 on a rebound of Ryan Pulock's shot, and Eberle gave the Islanders a 2-1 lead when his shot from beyond the right circle found its way between Rask's pads at 15:16.
New York outshot Boston 13-3 for the remainder of the period after Marchand's goal.
"I think from the 10-minute mark (of the first period), any puck below the goal line was a challenge for us to break out, whether it was miscommunication, just not executing, not getting there on time, their second guy beating our second," Bruins coach Bruce Cassidy said. "We just had a really tough time, and so we got hemmed in our end. It cost us three goals, really, today. The first three goals, we had puck possession, we just didn't execute the play. That's where our problems were tonight."
Bergeron tied it 2-2 at 16:51 of the second period on a wrist shot from the right circle after a cross-ice pass from Marchand.