The Bruins are winless in four games (0-3-1) for the second time this season. They were 0-2-2 from Nov. 5-12.
"Listen, we're all frustrated, but as a coach, you like how the 60 minutes transpired better than some of the other nights," Boston coach Bruce Cassidy said. "We're in the game. We're right there. We very easily could've won the game. Two or three things probably changed that, but in terms of the 60-minute effort, I think we're getting close to where we want to be."
With the Capitals (23-5-5) leading the NHL with 51 points and the Bruins (20-6-6) in second with 46 points, the game had a Stanley Cup Playoff feel. But the Bruins again couldn't find a way to defeat the Capitals.
Their lone win in their past 17 games against the Capitals (1-13-3) was a 1-0 victory at Washington on Feb. 3. Before that, the Bruins hadn't defeated the Capitals since March 29, 2014.
This season, the Capitals are 2-0-0 against the Bruins, including a 3-2 shootout win at Boston on Nov. 16.
"It's just one of those things," Boston forward Jake DeBrusk said. "I think every single team in the League has that. We did beat them actually last year here 1-0, so it's been officially done with. … It's obviously a team we understand we need to have our best, and it just didn't go our way tonight."
The Bruins won eight straight before a 4-3 overtime loss to the Chicago Blackhawks on Dec. 5, and they went 13 games without a regulation loss (9-0-4) prior to a 4-1 loss to the Colorado Avalanche on Dec. 7. But they thought their play was trending in the wrong direction before those streaks ended.
"It's coming back at us now," Cassidy said. "I think some teams outplayed us at the start of the year, but we made the plays when we needed to at the right time, played winning hockey when we did get the lead. Now it's going the other way a little bit, so you've got to battle your way out of it."
Getting their power play going would help. Boston went 0-for-5 with the man-advantage Wednesday and is 2-for-25 (.08 percent) over the past eight games.
The Bruins appeared to end their power-play slump when Patrice Bergeron knocked in his own rebound for a goal that would've increased their lead to 2-0 with 4:25 left in the first period. But the Capitals challenged for offside and video review revealed that DeBrusk entered the offensive zone a smidge before the puck, so Bergeron's goal was disallowed.
"We had the chances, especially first period," forward David Pastrnak said. "I think we had really good looks, we recovered the puck well and it just didn't go in for us. Then you get more power plays and the more you don't get the goals, it got a little bit away."
Still, the Bruins led 1-0 after one period thanks to Pastrnak's goal at 9:36. He beat goalie Braden Holtby high to the short side from the right circle to snap a four-game drought and increase his League-leading total to 26.