It was wild, it was weird and it was an Islanders overtime victory in Game 3, courtesy of a successful coach’s challenge, a two-goal rally and a clutch first-ever playoff goal by Thomas Hickey.

The diminutive defenseman’s quick shot past Roberto Luongo at 12:31 of overtime Sunday night gave the Islanders a 4-3 win over the Panthers and a 2-1 series lead in the first playoff game in Barclays Center history.

And it turned on the word of Islanders video coach Matt Bertani, who — after a seemingly back-breaking goal by Aaron Ekblad that was going to make it 3-0 Panthers at 4:08 of the second — radioed from his room off the Islanders’ locker room that it appeared Jonathan Huberdeau was offside while entering the Isles’ zone 11 seconds before Ekblad’s score.

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“What a call by Matty,” Frans Nielsen said. “It changed the whole game.”

Red-hot Panthers forward Reilly Smith scored off a rebound 2:25 in to quiet down a raucous crowd, and Smith set up Aleksander Barkov for a quick strike 1:11 into the second period for a 2-0 Florida lead.

Barkov fed Ekblad for that possible 3-0 goal and the building in Brooklyn went silent. In the 10 or so seconds the Islanders had to challenge, Bertani saw that Huberdeau’s skate entered the Isles’ zone a hair before the puck and radioed for the challenge.

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Linesmen Shane Heyer and Mark Shewchyk studied the video on a small tablet in the penalty box for several minutes before determining Huberdeau indeed was offside, and the goal was waved off. That brought the crowd to life and woke up the Islanders, who moved within a goal at 2-1 on Ryan Pulock’s slapper on a five-on-three 84 seconds later.

“You could feel it in the building when they called it no goal; everyone just picked up,” Hickey said. “I think Matty’s getting a pay bump after this one.”

Smith again made a superb move towards the Islanders’ net and Nick Bjugstad stuffed in the rebound to make it 3-1 Panthers at 7:23. The Islanders didn’t quit, though, buoyed not by their stars but by some youngsters who weren’t even on the squad two months ago.

After a strong shift by Alan Quine’s line, Pulock found Shane Prince racing down the slot and he beat Luongo at 11:48. Nielsen tied the score with a power-play goal at 16:55 of the second, sending the fans into a frenzy.

“Pully’s playing like a veteran,” Nielsen said. “It’s great to see a guy in his first year, his first playoff, playing with that kind of confidence.”

The third period and first half of overtime felt like a reset, with neither team gambling much after the wild and wooly second.

But as a strong shift by the maligned Islanders forward trio of Nikolay Kulemin, Brock Nelson and Josh Bailey neared its conclusion, Nelson worked the puck behind the Panthers’ net and Hickey — one of the smarter Isles defensemen — saw Kulemin go for a line change, meaning a forward could cover his spot as he darted down the slot.

Nelson hit him perfectly and Hickey beat Luongo. Of his 14 career goals, four of them — three in the regular season and one in the postseason — have been OT winners.

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“There’s not a guy on our team who plays as big as Thomas Hickey,” coach Jack Capuano said. “We were just resilient.”

And now, thanks to an unknown video coach and an unsung defenseman, the Islanders have the lead in the series.