The Flyers gave the Islanders two third-period power plays and, in essence, New York capitalized on both of them.
"Against a good power play like theirs, you're asking for trouble," said coach Craig Berube, whose team leads the NHL in two dubious categories: minor penalties (226) and penalty minutes per game (16.1).
Technically, Nelson's goal was not on a power play, but it was scored just after Adam Hall left the penalty box and he was not back in the play. That cut the Flyers' lead to 3-2 with 11 minutes, 44 seconds left in regulation.
With Steve Downie in the penalty box for an ill-advised holding penalty, Okposo tied the score at 3-3 with 2:58 to go. Frans Nielsen's backdoor pass bounced off Okposo's skate and past goalie Ray Emery, who made 40 saves and played admirably.
"You're not going to win a game playing with a man in the box," said winger Matt Read, who scored a pair of goals. "It's something we've kind of struggled with lately. We've let teams get back in the game and get momentum in the game. It's just a matter of not moving our feet and committing stupid penalties. We have to learn from this."
The Flyers, who only seem to win games lately when they are behind in the third period, had been 15-2-3 when taking a lead into the third.
"We weren't trying to play defensive; we were just getting outworked, I guess," Read said.
Read scored on a shorthanded breakaway 1:26 into the second period to give the Flyers a 1-0 lead.
Eight minutes later, John Tavares tied it when a puck deflected to him out front and he had a tap-in.
But Wayne Simmonds scored his 17th goal, depositing his own rebound, to put the Flyers ahead, 2-1, with 8:30 left in the second period. It gave Simmonds 12 goals in his last 17 games.
With 1:44 to play in the second, Read made it 3-1 with his second goal of the game and 13th of the season. Read blazed past defenseman Colin McDonald on the outside and then beat goalie Anders Nilsson with a crafty shot that went over his right shoulder to the short side.
Emery stopped Michael Grabner on a shorthanded breakaway in the first period and denied Matt Martin - who tried to finish a two-on-none break - early in the second period. With about six minutes left in the second, he was prone on the ice when he twice stopped Tavares out front.
"He stood on his head," Simmonds said.
The Flyers are 24-12-6 since their franchise-worst 1-7 start. They are 33-4-3 against the Islanders since 2007-08, but they felt they let a point slip away.
"They gained momentum with the penalties and power plays," Emery said. "Sometimes, they get you on your heels."