Cody McCormick, Jason Pominville and Thomas Vanek also scored for the Sabres, who passed the Capitals and grabbed sole possession of the Eastern Conference's eighth and final playoff berth with five games remaining.
Buffalo won a fifth straight contest with the help of Tyler Ennis, who contributed a pair of assists.
Washington dropped its fifth in seven games, managing only a single tally from Alexander Semin.
Braden Holtby started the game in goal but was yanked after yielding three scores on 18 shots. Michal Neuvirth relieved and stopped 11-of-13 shots the rest of the way.