Toronto went ahead 2-0 on a power-play goal by Nadri at 12:13 of the second. Dion Phaneuf passed the puck from behind the net in front to a wide open Kadri, whose shot beat Theodore on the glove side.
The Leafs stretched it to 3-0 less than two minutes later. Kadri passed the puck from the right side to MacArthur between the circles and he rifled the puck past Theodore on the stick side with 6:03 left in the period.
The Maple Leafs play four of their next six games on the road and are being careful to not get overconfident.
"We're still very much a work in progress," Maple Leafs coach Randy Carlyle said.
The Panthers didn't get a point after losing their last three games in overtime.
"It's not fun, we need to be better, we know we need to be better, the game plan's been put out there for us and we need to go execute it. We're not executing it," Panthers defenseman Brian Campbell said.
Notes: Kessel has all three of his goals and 10 of his 12 points on the road this season. ... The Maple Leafs are 20-21 on penalty kills over the last six games. ... Panthers F Kris Versteeg missed his third straight game with an upper-body injury.