The teams combined for five goals in the third, with Toronto holding on to a 5-2 lead to win its third in a row and 11th in 15 games.
Nazem Kadri's fifth goal in his past three games stood up as the eventual game-winner. He pounced on a loose puck at 10:18 and unloaded a slap shot from the high slot for his 10th goal of the season.
Phil Kessel had a goal and two assists for the Maple Leafs. It is the second time this season he has tallied three points in a game.
"They came at us pretty hard there at the end," Kessel said. "We were fortunate the sneak out a win."
He scored his sixth goal of the season with the man-advantage early in the third to give the Maple Leafs a 4-2 lead. At the time, it looked as though Toronto had staved off a Senators' rally which started when Zack Smith deposited a Chris Phillips' rebound behind James Reimer for his first goal of the season. Smith's marker at 1:40 pulled the Senators to within one, at 3-2.
As Ottawa gained momentum and started buzzing around the Maple Leafs' zone, Mika Zibanejad received a slashing penalty that led to Kessel's power-play goal at 3:42. His low wrist shot from the left circle went under Sens goalie Ben Bishop, who was unable to see the puck as James van Reimsdyk was blocking his view.
"He made a great screen there, and obviously the goalie didn't react fast enough," Kessel said. "It makes it tough on the defensemen when a guy like JVR goes hard to the net. Things happen and you get breaks."
However, the Senators refused to buckle and once again demonstrated the resiliency they have shown all season.
Colin Greening and Daniel Alfredsson scored goals 5:55 apart in the final 10 minutes of the third period, but Ottawa could not tally the equalizer despite pouring on the pressure in the final minutes.
"Zack Smith got a goal, Mika played well and got a goal, we had a lot of positive things happen in the game, along with some of the not-so-positive things," Ottawa coach Paul MacLean said. "At the end of the night, I thought we were very competitive here on the road and we obviously have to continue to push ourselves to be better."
Reimer held the fort when it counted, stopping 15 of 18 shots in the third period while his team only countered with four shots of its own. Reimer finished with 39 saves.
"You never want to get ahead of yourself, so maybe that is the good thing about having a dampering win, for lack of a better word. It keeps you from getting too high," Reimer said. "I think we weren't our sharpest tonight, but we are a good team. We got confidence in each other and we know we can get the job done and we did tonight. We found a way. That is perhaps the most important thing."
Toronto was up 3-1 heading to the third period after the teams traded goals in the second.
The home side went up 3-0 at 1:20, when van Riemsdyk scored his team-leading 12th goal of the season. Tyler Bozak stripped Senators defenseman Marc Methot behind Bishop before getting the puck to Kessel at the side of the net. Bishop was able to kick out Kessel's shot, but the rebound came to van Riemsdyk, who was alone in front.
The three-goal cushion was short-lived, as Zibanejad buried a rebound from Sergei Gonchar's point shot at 2:48. Toronto defenseman Carl Gunnarsson tried desperately to fire the puck out of the crease, but he had to contend with Zibanejad and Erik Condra in the blue paint. It was Zibanejad's fifth goal of the season.
Bishop looked much stronger than he did in the first period, settling down to stop 13 of the 14 shots he faced. He ended up with 23 saves.
The Maple Leafs held a 2-0 lead after one period on the strength of two goals in a 56-second span.
Tyler Bozak opened the scoring at 6:24, whacking in Kessel's centering pass as he was skating up the middle toward Bishop.
Things did not get any easier for the injury-depleted Senators when Jay McClement scored his second goal in as many games at 7:20. McClement now has four points in his past five games.
Nikolai Kulemin initially looked to take a shot near the edge of Bishop's crease but had his stick lifted by Kyle Turris. The puck traveled straight to McClement, who found the back of the net as he cruised through the slot.
The teams didn't waste any time getting reacquainted in their third meeting of the season.
At 26 seconds after the opening faceoff, Toronto's Frazer McLaren knocked out Dave Dziurzynski when the two fought in the Maple Leafs' zone. Dziurzynski, a rookie forward playing in his 10th NHL game, had to be helped off the ice and was diagnosed with a concussion. The Senators gave no further update on his status after the game.
Dziurzynski made his NHL debut Feb. 16, the prior time the Senators played at the Air Canada Centre.
"You never want to see that happen; I hope he is ok," McLaren said. "I asked the doctor between periods just to get word that he was alright. It is just an unfortunate incident that happens. I'm not quite sure how it happened, it happened so quick. … I must have just caught him. Sometimes if you catch someone in the right spot, it doesn't necessarily have to be the hardest punch. I have been on the reverse side of that. I've been knocked out before. I've been on the other end of it, so I know how it feels as well."
Milan Michalek had an assist in 18:22 of ice time in his return to the Senators. He had not played since injuring his knee prior to a game against the Pittsburgh Penguins on Feb. 13.
Senators forward Mark Stone made his regular-season debut after playing one game in the 2012 Stanley Cup Playoffs. He finished with a minus-1 rating in 15:14 of ice time.