Ales Kotalik had a goal and two assists while Maxim Afinogenov and Thomas Vanek added a goal and assist each for the NHL's top-scoring team. Brian Campbell also scored in a game that was decided before it was 11 minutes old.
Buffalo needed only nine shots to build a 6-0 lead when Vanek, from the right circle, banked a wrister in off Capitals defender Brian Pothier in front with 9:03 left in the first period.
The Sabres (26-7-3) improved to 2-2-1 in their past five games, including a 3-2 overtime loss at St. Louis on Saturday.
Alex Ovechkin, booed loudly after he cut the Sabres' lead to 6-2 late in the second period, Chris Clark and Kris Beech scored for the Capitals (16-13-7), who had a four-game road winning streak snapped while opening a stretch of four games in five nights.