Beauvillier scored on a rebound in the crease after Nick Leddy's shot trickled under the arm of goalie Jaroslav Halak. It was Beauvillier's second overtime goal in as many games.
"Well first of all, it's a privilege to be out there in overtime, to have the chance to make your team win," said Beauvillier, who scored the winner in a 2-1 victory at the Philadelphia Flyers on Monday. "It shows the trust that the coaching staff has in you, and I take a lot of pride in that, and I just want to do my job out there. I got fortunate over there with the loose puck, but I thought we did a really good job tonight just staying with the process and coming from behind."
The Bruins (16-8-5) were playing for the first time since March 18 after having two games postponed because of NHL COVID-19 protocol. Tuukka Rask made six saves in the first period but didn't return after the intermission because of an upper-body injury. He was replaced by Halak, who made 17 saves.
There was no update on Rask's status after the game.
"[We] didn't defend well enough in front of our net," Boston coach Bruce Cassidy said. "Had to switch goalies, sure it wasn't easy on 'Jaro' to go in a situation like that, and they finished around the front of the net. We could've been harder, could've used an extra stop. Got a point out of it. We were in a position to get two. Again, they played winning hockey in the third period better than we did."
Jean-Gabriel Pageau had a goal and two assists, and Semyon Varlamov made 29 saves for the Islanders (22-8-4), who have won three in a row and are 5-0-0 against the Bruins this season.