Danny Briere scored the only goal in the shootout, Boucher stopped all three Washington attempts and the Philadelphia Flyers wasted a two-goal lead in the third period before beating the Capitals 5-4 on Saturday night.
"It's just nice to win," said Boucher, whose last victory came on Oct. 23. "Obviously, you get a two-goal lead in the third and you want to nail it down. It didn't happen."
In the shootout, Boucher blocked Nicklas Backstrom's drive, gloved Alex Ovechkin's shot and slid as Alexander Semin's try glanced off the crossbar. Briere, the second Flyers shooter, put the puck between Michal Neuvirth's pads.
"Backstrom was going high glove and I got a piece of it," Boucher said. "Ovechkin, I think for the most part, is a shooter. Earlier in the game, I showed poke-check on him, made him deke and he hit the crossbar. So I certainly wasn't going to do that again. ... I was set on him shooting. He's a good shooter and I had a read on it."
That left Semin, who couldn't convert his backhand try.
"Thank goodness," Boucher said. "As long as it doesn't go in."
Philadelphia went ahead 4-3 with 6:07 remaining on Andreas Nodl's goal from between the circles. But Eric Fehr scored on a one-timer from the right circle on a power play with 38.8 seconds left in regulation after Briere had been whistled for high-sticking.
"We need to stay out of the box, obviously," said Philadelphia defenseman Chris Pronger, who had two assists.
All three of the Capitals' third-period goals were on power plays.
Claude Giroux, Mike Richards and Jeff Carter also scored for the Flyers, who handed the Capitals their second home loss in 12 games in a duel between the top teams in the Eastern Conference.
"It's one thing to beat the lower-seed teams," Briere said. "But we have to start showing we belong amongst the best."
Marcus Johansson, Nicklas Backstrom and Jason Chimera had the other goals for Washington, which lost a second straight game for the second time this season.
Washington was coming off a 5-0 loss in Atlanta on Friday, while the Flyers' last game was an 8-7 home loss to Tampa Bay on Thursday.
"Both teams were coming off games that they probably didn't feel very good about themselves," Capitals coach Bruce Boudreau said. "I think two very proud teams wanted to get back and show that they could play."
The Capitals squandered two early scoring chances, clanging shots off the right post and the crossbar, before Johansson's second goal of the season gave them a 1-0 lead 8:50 into the game. Johansson darted down the slot and flicked a wrist shot past Boucher.
Giroux's team-high 11th goal tied it at 13:11 of the second period. With Washington's Brooks Laich off for goaltender interference, Giroux redirected Pronger's center-point drive at the left post.
Philadelphia went ahead on Richards' goal late in the second. Scott Hartnall, tied up at the left post, couldn't get a shot off, and shoveled a pass to Richards, who cut in from the right circle.
Carter scored midway through the third to make it 3-1. He skated into the zone and uncorked a wrist shot from between the circles with 10:20 left.
Backstrom and Chimera scored on power plays 28 seconds apart, tying it at 3. Backstrom skated to the right post to knock in Ovechkin's rebound with 8:57 remaining, and Chimera banged in his own rebound from the same spot.
Nodl converted a centering pass from James van Riemsdyk after Richards made a nice play to keep a clearing pass in the zone. Fehr's goal came off a behind-the-net feed from Laich.
Washington played the final 1:48 of overtime a man down after an interference minor against Backstrom.
"It's just unlucky that we didn't get two points, but I think we struggled hard and we fought for it," Johansson said.