Jacob Markstrom made 13 saves for Florida, which played its final home game of the season. The Panthers clinched the worst record in the NHL for the first time in franchise history.
Toronto snapped out of a 1-3-0 slump coming into the game, scoring four goals on just 17 shots.
The Maple Leafs can't finish lower than sixth in the Eastern Conference.
The Maple Leafs took a 3-0 lead on Kessel's first goal of the game. Kadri brought the puck down from his own end on a 2-on-1 break. He slipped the puck over to Kessel on the right side and he wristed the puck past Markstrom at 1:41 of the second.
Kessel scored his second goal three minutes later when he grabbed a loose puck in front of the crease and poked it in at 4:41 to make it 4-0. Kessel has nine goals in his past 10 games and 19 for the season.
The Maple Leafs took a 1-0 lead on Komarov's goal in the first period. Jay McClement brought the puck out from behind the net and swept a pass across to Komarov in the right circle. His wrist shot got past Markstrom at 5:39.
Toronto stretched its lead to 2-0 when MacArthur scored. MacArthur brought the puck down from his own zone end and passed to Matt Frattin in the right circle. Frattin's shot was blocked, but MacArthur poked in the rebound at 14:32.
Notes: Toronto C McClement played in his 600th NHL game. ... Florida D Tyler Strachan returned after missing four games. ... C Quinton Howden returned after missing Tuesday's game due to illness.