WASHINGTON -- The season is barely half over, but it was hard not to picture the top two teams in the Eastern Conference meeting again in the playoffs.
The Bruins began the day with the NHL's best record and finished it nine points ahead of Washington for the top mark in the East.
"It was a playoff-type atmosphere and game," Washington coach Bruce Boudreau said.
He isn't ready to think about a possible six or seven-game series with a potential trip to the Stanley Cup finals on the line.
"It's too early to talk about the playoffs," Boudreau said. "I hope to get to that point. I hope to get to May."
Boudreau watched Semin take the puck at the Capitals' blue line, streak down the ice, and fire a shot past goalie Tim Thomas at 11:48. It was his 18th goal of the season and fourth in four games.
The unassisted goal broke a 1-1 tie and snapped the Bruins' four-game overall winning streak. Boston had won seven straight on the road.
Semin skated right past the Washington bench, and Boudreau was surprised he shot. So was Thomas.
"I didn't know Semin was just going to come down and shoot it," Thomas said. "There's not that many times when a guy has that much time to wind up for a slap shot like that."
The Capitals, who had lost their previous two home games after going 18-1-1 in their first 20, dominated play in the third period before Semin broke through.
"I wish he'd shoot more," Boudreau said.
Jose Theodore stopped 23 shots for his second straight win. Washington beat Pittsburgh 6-3 on Wednesday to end a three-game slide.
"It was a playoff game, I think -- that mentality. Two really good teams," Theodore said. "Obviously, you didn't want to make a mistake."
The Bruins, who hadn't lost on the road since their previous game in Washington on Dec. 10, were trying to tie their longest winning streak away from home in nearly 16 years.
"We knew it was going to be one of those tough games," Boston coach Claude Julien said. "It doesn't take much sometimes to differentiate between winning and losing."
Thomas, who entered the game with an NHL-leading .930 save percentage, had won 10 of his previous 11 starts.
The Capitals had a scary moment late in the game when John Erskine was penalized for elbowing with 1:41 to play. The Bruins pulled Thomas with 1:10 left, giving Boston a two-man skating advantage, but Washington killed the penalty, allowing only a weak shot on Theodore moments before the final horn sounded.
Marc Savard gave Boston a 1-0 lead at 1:49 of the second period. With Washington's Milan Jurcina in the penalty box, the Bruins controlled the power play. Just 29 seconds later, Savard fired a shot from 25 feet past Theodore for his 15th goal.
Just 1:10 later, Mike Green tied it when he faked Thomas in front of the Boston net, and slapped in a shot for his 12th goal.
Capitals RW Chris Clark was a healthy scratch for the second straight game. ... C Boyd Gordon (back spasms) and D Shaone Morrisonn (lower body) were out for Washington. ... Boston LW Milan Lucic missed his fifth straight game due to a shoulder injury. ... D Aaron Ward was out for the second straight game because of a charley horse. ... The Capitals have never lost three straight at home under coach Bruce Boudreau, who took over last season.