Morgan Frost extended the lead to 3-1 at 13:41, finishing a give-and-go with Owen Tippett.
The Flyers outshot the Islanders 11-6 in the second.
“I think our turnovers killed us,” Horvat said. “We were turning pucks over at the wrong time, and especially, feeding their transition. They're a quick team that likes to feed off the rush, and we just let them have it. And it just wasn't good enough by us tonight.”
Mathew Barzal cut it to 3-2 at 30 seconds of the third period. He scored under the blocker from the right circle off the rush.
Cam York gave Philadelphia a 4-2 lead at 5:16 when he scored to the blocker side from the left circle.
Anders Lee brought New York within 4-3 at 17:16 with a power-play goal when Horvat’s shot from the point banked off him and in. The Islanders were on a 6-on-4 with Sorokin pulled for the extra attacker.
Noah Cates scored an empty-net goal at 18:48 for the 5-3 final.
NOTES: Frost extended his point streak to five games (six points; four goals, two assists). ... York ended a 17-game goal drought. … Lee reached the 20-goal mark for the fourth straight season and the ninth time in his 13 NHL seasons.