Mistakes early in the first period put the Bruins in the hole, as the Capitals capitalized on self-inflicted mistakes to jump out to a 2-0 advantage.
"Obviously a tough start," Bruins forward David Pastrnak said. "It started with me taking a penalty (while we were) on the power play, and them getting a shorthanded goal. Credit to us, we battled back.
"We stick up for each other. There's been fights, amazing fights. We stick together as a group, fight to get back in the game. We were right there going into the third."
With the Sabres win over the Senators, Boston fell to dead last in the conference
David Pastrnak shone with two goals in the game, taking his season total to 37 with seven games left. Morgan Geekie assisted both of Pastrnak's goals with primary assists.
Meanwhile, Alex Ovechkin moved closer to Wayne Gretzky's record for career goals, netting his 38th goal of the season on a power play in the first period. The goal is his 891st in his career, and it leaves him three goals behind Gretzky's mark.
Now, the Bruins head to Montreal to meet the Canadiens at the Bell Centre on Thursday night, with the puck being dropped at 7 p.m. ET.