Dominic Moore and Mikhail Grabovsky also scored, and Vesa Toskala made 22 saves for Toronto. The Maple Leafs have won two straight and earned points in five of six games.
"We have a chance to be over .500 in the first month," Toronto coach Ron Wilson said. "I don't think anyone thought that was possible with the schedule we have."
Shean Donovan and Dean McAmmond scored for Ottawa.
The latest Battle of Ontario had a feisty edge to it, with both teams throwing their weight around from the opening faceoff.
Toronto rookie defenseman Luke Schenn took part in his first NHL fight less than a minute into the game, after Senators agitator Chris Neil caught Matt Stajan with a knee-on-knee hit. The 18-year-old Schenn held his own against a guy who had already fought 117 times in his career.
"Luke's been there for me," Stajan said. "It seems like every time I get hit, he jumps in. ... I was looking over my shoulder and saw it was Neil. It shows a lot about him that he doesn't care. He's a tough kid. I would return the favor if anyone was able to knock him over but he's a pretty big boy."
Perhaps that sparked a Leafs team that threw all it had at Ottawa backup goalie Alex Auld, given his second consecutive start by coach Craig Hartsburg.
Aided by three power-play opportunities, Toronto had 21 shots on goal in the first period and took a 1-0 lead to the dressing room. Moore opened the scoring at 14:14 while the Leafs had a man advantage by chipping the puck over a sprawled Auld as several players converged on the crease.
"I don't think we played the kind of game early that gave us a chance to win," Senators coach Craig Hartsburg said. "We did not have enough. They were the better team tonight. They were quicker, stronger on the puck and more competitive."
Toronto went ahead 2-0 with Grabovski's long-awaited first goal of the season at 2:15 of the second period. The flashy Belarussian had grown visibly frustrated during his goal-less drought but was smiling widely after taking a nice pass from Niklas Hagman behind the net and lifting a hard wrist shot over Auld's shoulder.
The Maple Leafs were dominating at that point and had Ottawa on the ropes. However, Donovan soon got his team back in the game by tipping Alexandre Picard's shot past Toskala to make it 2-1 at 4:06.
Ponikarovsky restored the two-goal lead at 13:37 of the third period after a scramble in front of Auld before McAmmond scored short-handed at 19:11 to set up a frantic finish. Toskala held strong as the Daniel Alfredsson-Dany Heatley-Jason Spezza trio pushed for the equalizer.
"Even with the lead now, we still kept skating and we didn't turn the puck over," Toskala said. "I would say that was our smartest game so far."
Notes: Jonas Frogren was scratched for the Leafs, making him the team's seventh healthy player to sit out a game this season. ... Luke Richardson sat out for the Sens. ... Senators defenseman Filip Kuba has a point in all eight games this season.