Okposo, who assisted on the Islanders' two goals in regulation, scored on a wrist shot after bringing the puck up through the neutral zone to the right circle.
Brandon Dubinsky scored both Rangers goals and Henrik Lundqvist made 19 saves.
Nielsen scored the first goal of the game on a set-up from Okposo at 7:45 of the first period. The Islanders went ahead 2-0 when Okposo chipped a pass to Comeau, who scored unopposed.
The Rangers made it 2-1 at 6:07 of the third period, then tied it on Dubinsky's tip-in at 19:13.