Goals by Alexandre Giroux and Alexander Semin staked Washington to a 2-0 lead after the first period.
Semin added two assists for the Capitals, whose losing streak was the longest since they dropped 13 straight from Oct. 11-Nov. 11, 1981.
Andrew Raycroft was beaten five times on 33 shots for the Maple Leafs, who had won their previous two games.
Toronto could not gain any ground on the New York Islanders or Carolina Hurricanes, who hold the seventh and eighth spots in the Eastern Conference, respectively.
Notable deaths of 2014 [PHOTOS]