Ryan Dzingel scored for the Senators, who played their first game since trading defenseman Erik Karlsson to the San Jose Sharks on Sept. 13.
"Until the very end our guys pushed," Senators coach Guy Boucher said. "There was a lot of good things from a lot of players. I really liked the attitude on the bench. It was terrific."
Matt Duchene took the puck away from Nazem Kadri and fed Dzingel to give Ottawa a 1-0 lead 21 seconds into the first period.
"I just go out there, try to work with [Matt] and try to understand where he wants me and where he wants the puck," Dzingel said.
Andreas Borgman gave Toronto a 2-1 lead at 6:34 of the first. The defenseman started the sequence when he dropped the puck to Trevor Moore in the Maple Leafs zone. Moore fed a stretch pass to Emerson Clark, who passed to Borgman between the circles for a one-timer.
Curtis McElhinney (12) and Garret Sparks (21) combined to make 33 saves for Toronto. Condon (18) and Hogberg (eight) made 26 for Ottawa.
"I thought our [defensemen] played well, our forwards played well and our goalies were outstanding," Rielly said.
The Maple Leafs and Senators played at Lucan Community Memorial Centre, which received $250,000 in upgrades after earning the highest number of votes to win Kraft Hockeyville Canada 2018.