Kerfoot made it 2-0 at 8:06 when he one-timed a pass in the slot from William Nylander, who stole the puck from Shane Pinto in the left-wing corner.
"It wasn't the start we wanted," Senators forward Drake Batherson said. "In the second period, I thought we pressed and were back into the game there, but they got a big goal late. We'll bounce back tomorrow against the Dallas Stars and have a better one."
The Senators got within 2-1 at 17:42 when Norris scored on the power play. Ottawa then had a possible tying goal overturned by a review for offside with five seconds left in the period.
"That was a nice call (to go our way) for sure," Campbell said. "Coming into the third if it was 2-2, it's a whole different ballgame, so regardless, we were up 2-1 and I thought the guys came out and played exactly how we needed to play to win the game in the third and made my job easy."
Bunting made it 3-1 at 7:57 of the third period when he pulled up on a scrambled 2-on-1 with Kerfoot, skated around defenseman Victor Mete and shot from the right face-off dot. The 26-year-old played his first two NHL seasons for the Arizona Coyotes before signing with Toronto this offseason.
"Whether he's scoring or not, he's competing at a very high level; he's engaged in the game and every shift," Maple Leafs coach Sheldon Keefe said. "He wants to score, everybody wants to score, but it's very obvious he's not afraid to go to the areas where the goals are more likely to happen."
Alexander Bishop, a 24-year old who plays for the University of Toronto and played 72 games in the Quebec Major Junior Hockey League from 2014-17, signed an amateur tryout contract to back up Campbell. The Maple Leafs were unable to recall a goalie from Toronto of the American Hockey League due to NHL salary cap constraints.
"We were chatting to him and talking him up and making sure he felt comfortable," Simmonds said. "Our team is all about unity, fighting for one another and being one for all and all for one."
NOTES: Maple Leafs goalie Petr Mrazek is expected to be out 14 days with a groin injury sustained Thursday against the Senators. Goalie Michael Hutchinson will be recalled from Toronto of the American Hockey League and join the Maple Leafs at practice Sunday. ... The Senators were without forward Brady Tkachuk for a second consecutive game after he signed a seven-year contract Thursday. It is unknown when he will make his season debut.