James Reimer turned aside 29-of-30 shots for the Leafs, who entered the contest eight points behind eighth-place Washington in the Eastern Conference with 11 games remaining.
The Senators, meanwhile, fell into second place behind Boston in the Northeast Division.
Colin Greening scored Ottawa's only goal and Ben Bishop supplied 15 stops for the Senators, who hold the seventh playoff berth in the East.
Beyonce flaunts bikini body, Blue Ivy in vacation pics
Benedict Cumberbatch's dramatic reading of R. Kelly lyrics is just what you need