The Capitals, who beat the Bruins 10-2 in Washington on Monday, were in line to win their fifth in six games but were whistled for five straight penalties -- three at once to Brashear -- that cost them the game.
Brashear got a double minor for high-sticking and had an extra 2 minutes tacked on with 6:41 remaining when he punched Boston defenseman Shane Hnidy in the face after the whistle. John Erskine went off for hooking 1:13 later and Tom Poti was called for slashing with 2:56 left to create an extended two-man advantage for the Bruins.
"Sometimes that's how it goes," Brashear said. "You can't lose your focus and you can't lose your cool. He was coming at me and I guess I lost my cool a little bit."
"Obviously I was a little shocked to take a punch like that," Hnidy said. "Frustration gets the best of players. It's a game of emotions."
"I admit Brash's penalties were dumb," Washington coach Bruce Boudreau said. "A guy that's been in the league that long should know that."
The Bruins halted a three-game losing streak and moved back in front of the New York Rangers for sixth place in the Eastern Conference. Those teams will meet Sunday at Madison Square Garden.
"We got pushed around the last time in Washington, and today we were ready for whatever happened," Bruins coach Claude Julien said.
Washington, which entered the day in 10th place -- four points behind Philadelphia and the postseason cutoff in the East -- is trying to become the first team to rally from 14th to make the playoffs.
The Capitals grabbed a 1-0 lead when Brooks Laich scored on a rebound after Alex Ovechkin recorded consecutive shots 6:17 into the game. Ovechkin fired a wrister from the left circle and charged in for the rebound before Laich beat goalie Alex Auld from the edge of the crease.
Just over a minute later, Chara was whistled for interference when he knocked Ovechkin's stick out of his hands and into the netting above Boston's goal. A fan pulled the Washington star's stick through a hole at the bottom, but the NHL scoring leader got it back from an usher.
Ovechkin had three goals, to surpass the 50-goal mark for the season, and two assists against the Bruins on Monday.
Capitals forward Matt Cooke was given a major penalty for kneeing and was ejected from the game in the second period after he stuck out his left leg out in a collision with Boston defenseman Bobby Allen.
Allen injured his left knee and was helped to the locker room, but returned later in the period.
"Look at Matt Cooke's penalty. That guy (Allen) didn't miss a shift," Boudreau said. "He got carried off like he was going to get his knee amputated and then after the five-minute penalty, he was back on there. It's anger right now, and you have to watch what you say. We're angry that we lost a game we thought we should have won."
- Washington goaltender Olaf Kolzig's next win will be his 300th in the NHL.
- The Bruins' longest skid of the season came in December when they lost six straight.
- The Bruins recalled defenseman Matt Lashoff from Providence (AHL) and he traveled with the team for Sunday's game at New York.