Washington's third line of Jason Chimera, David Steckel and Matt Bradley provided the scoring and the spark against the Sabres.
Bradley and Steckel each scored a goal, with Chimera providing assists both times. Bradley also added an assist on Steckel's goal for his first multiple-point game since Jan. 7.
"Guys like Stecks and Brads work hard all year and they don't often get rewarded for their work," Chimera said. "It's nice to get a reward, get some goals."
Nicklas Backstrom also had an early goal as the Capitals built a 3-0 lead in the second period before holding off the Sabres' comeback attempt, which started when Derek Roy and Jordan Leopold scored less than a minute apart in the second period for Buffalo.
"After the third goal we really turned the corner," Buffalo coach Lindy Ruff said. "We made a lot of good plays, won the battles to create some of those chances. I didn't like our start. Obviously, that hurt us."
The Capitals have had some trouble protecting early leads in the past few games, including Saturday's 3-2 overtime loss at Buffalo.
"It hasn't been fun playing games when you're up and you let them come back," Washington defenseman Karl Alzner said. "We've been talking about it, and tonight was a game where it seemed no one was getting down. Everyone stayed up."
The Capitals got up early when two Buffalo penalties within 13 seconds gave the Capitals a 5-on-3 chance midway through the first period.
Alexander Semin found Backstrom with a cross-ice pass through the crease, and Backstrom hammered it home from the right side of the net for his sixth goal of the season at 12:31.
Semin's assist and his empty-net goal in the final seconds extended his point-scoring streak to nine games, the longest by a Capital this season.
The third line took over after the opening goal, giving the Capitals a 2-0 lead a few minutes later on Bradley's second goal of the season.
Chimera made a between-the-legs pass from behind the net and facing the boards, directly to Bradley in front of the goal. Bradley's shot trickled through goaltender Ryan Miller's pads to extend the lead.
Another Chimera pass from behind the net -- this time facing the play -- led to the Capitals' third goal, as he found Steckel in front at 2:45 of the second period.
"They were really good," Washington coach Bruce Boudreau said. "I thought they were our best line."
Buffalo made its push later in the second period. Roy put the Sabres on the board with a power-play goal at 12:07, and 48 seconds later Leopold put in a loose puck to make the score 3-2.
Leopold's score was set up when Rob Niedermayer tried to pass to Cody McCormick in the left circle, but Capitals defenseman Jeff Schultz contested the pass. As the two players were tied up with the puck sitting behind them, Leopold skated in for the shot.
Buffalo had more offensive chances after the flurry, including power plays late in the second and third periods, but Washington goalie Michal Neuvirth made 31 saves -- 10 in the third period -- for his 12th victory of the season.
"He played well in the third," Sabres forward Jason Pominville said. "We can give him credit or we can say that we didn't find ways to score. It's a little bit of both. It's frustrating, but we know we dug ourselves a big hole."
Washington, which has a league-high 29 points, improved to 10-1-0 at the Verizon Center.
"When we try to be fancy and do things we shouldn't, that's when we get in trouble," Bradley said. "We're just playing a simple game. That's what we did tonight."
Washington C Tomas Fleischmann missed his first game this season as a healthy scratch. "It's his turn," Boudreau said before the game. ... D Tom Poti missed his third straight game and 11th of the past 12. He played Thursday after sitting out eight games because of a groin problem and hasn't seen action since. C Boyd Gordon (leg) returned after missing two games. ... Buffalo C Nathan Gerbe returned after missing eight games with a fractured jaw. ... Buffalo ended a team-record five-game streak of overtime games. Buffalo was 4-0-1 in that span.