Simon Holmstrom scored twice, and Ilya Sorokin made 28 saves for the Islanders (4-3-1), who have alternated wins and losses through their first eight games.
New York played most of the game without forwards Calum Ritchie and Matias Maccelli, who were each injured in the first period. Ritchie left after just one shift with a lower-body injury, and Maccelli exited at 16:36 after falling awkwardly on his left knee when he was tripped by Darren Raddysh. Maccelli put minimal weight on the leg as he was helped off the ice by two teammates.
Sergei Bobrovsky made 16 saves for the Maple Leafs (3-4-2), who are 1-2-2 in their past five games.
Toronto was without forward John Tavares, who is week to week with a lower-body injury he sustained in a 5-4 overtime loss to the Buffalo Sabres on Thursday.
Anthony Duclair put the Islanders ahead 1-0 at 8:18 of the first period. He took a backhand pass from Jean-Gabriel Pageau, who was along the right boards, stepped to his left on Nick Paul in the slot, and beat Bobrovsky low to the glove side.
Horvat made it 2-0 at 18:33 of the second period, putting in a rebound in the slot after Bobrovsky made a right pad save on Kyle Palmieri.
Colton Sissons cut it to 2-1 at 3:54 of the third period with a redirection of Troy Stecher's one-timer from the right point.
Holmstrom pushed it to 3-1 at 14:08, taking a pass from Horvat and shooting past Bobrovsky’s glove from the slot. He then scored into an empty net at 17:55 for the 4-1 final.
