Perreault's third goal of the game came 7:18 into the third period when he put in a rebound off Roman Hamrlik's shot to give Washington the lead. The score broke a 3-all tie and brought hats raining down onto the Verizon Center ice.
"It was outstanding," forward Matt Hendricks said. "Kid's been working extremely hard all season. He's been in and out of the lineup. He comes to the rink with that smile on his face and he's got a great personality, great guy to be around. I feel great for him. I'm so happy. Everybody else in this room I'm sure feels the same way."
The Capitals were without Ovechkin, who was serving the first game of a three-game suspension for a hit on Pittsburgh defenseman Zbynek Michalek in Washington's loss Sunday. Ovechkin also announced Tuesday he would skip the NHL All-Star Game, saying, "My heart is not there."
Washington was already missing another key offensive player: center Nicklas Backstrom, who missed his 10th straight game after being elbowed in the head.
"You're not going to replace Alex, but as a committee we're going to have to get the goals," Washington coach Dale Hunter said before the game. "We need people to step up."
Perrault certainly did.
His first goal came at 2:55 in the second period, 41 seconds after Cody Eakin scored Washington's first goal. Perreault brought the puck down the center of the ice, passed to Alexander Semin on the right side, and Semin sent it back to Perreault, who was between the circles. Perrault flipped the puck past Boston goalie Tuukka Rask after he had moved to cut off a possible shot by Semin.
The teams then traded scores off turnovers. Seguin picked off a pass from Capitals defenseman John Carlson in Washington's zone and scored at 12:21 in the second.
Perreault put the Capitals ahead again about 2 minutes later, stealing a pass in the middle of the ice and converting on a breakaway for his second of the game.
"That breakaway was one of my nicest goals," Perreault said. "But that third one, when you get that hat trick, it's awesome. The crowd gets into it, and the hats are going onto the ice -- it's just awesome."
Perreault was also at the center of Boston's goal late in the second period which tied the game at 3, when he was whistled for a hooking penalty with about 3 minutes to play in the period. Boston took advantage as Marchand banged in a rebound with 2:18 left.
Perreault's third goal gave Washington the lead, and Dennis Wideman had an empty net goal in the final minute to secure the victory.
"Not a very good game for us to end with before the break, no doubt," said Boston coach Claude Julien. "Probably the positive thing is we've got five days to think about that, and come back hopefully refreshed, rejuvenated and playing with a lot more energy."
While the Bruins head into the All-Star break disappointed, the Capitals ended the first half of the season on a high note after struggling at times this season.
"I think it was one of the biggest (wins) of the year," Hendricks said. "We didn't have all of our skill in the lineup, we didn't have our leader in Ovi. We really knew we had to play as a team tonight, come together as a great hockey team, and I think we did that."
Boston RW Nathan Horton sat out his first game of the season with what Julien termed a "mild concussion." Julien said he hoped Horton would be able to return after the All-Star break. ... Boston G Tim Thomas, who skipped Monday's White House ceremony honoring the team's Stanley Cup win last season, did not play. ... Hunter said he didn't expect Ovechkin to be handed a three-game suspension. "I was surprised it was as harsh as it was," the coach said before the game.