Trevor van Riemsdyk scored his first goal with the Capitals (6-0-3), who led 3-0. Vitek Vanecek made 40 saves in Zdeno Chara's first game with Washington against his former team.
"He's been unbelievable so far," Tom Wilson said of Vanecek. "He's given us a chance to win every night and more. Obviously, a lot of adversity the first little bit here, and he's been our best player every night, and we're pretty lucky to have him back there right now."
Charlie McAvoy scored the tying goal with 58 seconds left in the third period for the Bruins (5-2-2), who had a four-game winning streak end. Tuukka Rask made 18 saves, and forward David Pastrnak had an assist playing 20:29 in his season debut after having hip surgery Sept. 16.
"I thought we were the better team, to be honest with you, if you look at the overall game. At the end of the day, we made a few mistakes," Boston coach Bruce Cassidy said. "They're a team that can capitalize in a hurry. Got some guys that can score. But you need saves, too, to pick you up, too, in some of those instances. We are a young team. We've talked about that. We make some mistakes at times."
Ovechkin did not play the final 6:50 of the third period.
"As soon as the overtime started, I thought he might be fresh, so we put him out there and he delivered," Washington coach Peter Laviolette said. "For me, it was a good first start for him. I thought he got better as the game went on."
The Bruins pulled within 3-2 at 6:03 of the third when McAvoy skated behind the goal line and, just before going behind the net, passed in front to Brad Marchand.
"It's funny the way things work out," Marchand said. "I was out of position there. I wasn't where I was supposed to be. [McAvoy] made a great play, drew everyone to him and I was kind of left all alone, but I wasn't supposed to be there, so I got lucky."
