Tom Wilson opened the scoring for Washington with 2:42 remaining in the first period. Casey Wellman doubled the Capitals' lead with 1:11 left in the second, but Justin Florek got the Bruins on the scoreboard 27 seconds later to make it 2-1.
"The guys have had a lot of hockey in a short amount of time," Capitals coach Adam Oates said. "Tomorrow, they're getting their first day off, so I think the guys were a little tired today. They got through the game and we got to the shootout which was good, because the fans like that."
Chris Kelly tied the score for the Bruins 7:54 into the third period.
"Wasn't the prettiest, wasn't as entertaining as you probably would like it to be," Bruins coach Claude Julien said. "But we found a way to win; comeback win, also."