Charlie McAvoy scored twice for the Bruins (37-23-6), who were 0-3-4 in their past seven games away from TD Garden. Jeremy Swayman made 25 saves for Boston, which holds the first wild card from the Eastern Conference, one point ahead of the Detroit Red Wings.
Rasmus Sandin had a goal and an assist for the Capitals (33-27-8), who trail the Red Wings by five points for the second wild card. Logan Thompson made 31 saves.
Matt Roy gave the Capitals a 1-0 lead at 1:15 of the second period when he received pass at the right point from Sandin, skated down and scored with high glove-side slap shot from just above the right circle.
Swayman kept the Bruins within one when did a split and made a right skate save against Sandin on a short-handed breakaway attempt at 4:04.
McAvoy tied the game 1-1 at 11:57 with a one-timer through traffic in front from the top of the zone off a pass from David Pastrnak.
Sandin gave the Capitals a 2-1 lead at 3:12 of the third period, scoring from the left point on a slap shot over Swayman's right shoulder through a screen.
McAvoy tied it 2-2 at 10:09 from the slot when he redirected Pavel Zacha's shot from the left point.
