There is poise under pressure, and then there is this.

What the Islanders did during their breathtaking 4-3 overtime win against the Penguins in Game 1 of their first-round playoff series on Wednesday night at the Coliseum was show that this stage is not too big for them. No bit of adversity buckled their knees, no bad call or lengthy review wore on their nerves, no late goal from the team across the way laden with championship pedigree ruined their spirits.

There is resilience, and then there is Mat Barzal stick-handling in front with no one around him like it’s a game of pond hockey instead of his first postseason game. More, it was overtime, and he was “overstaying my welcome,” as he described it, before hitting the post with a backhand. And then as the 13,917 all sucked in a collective breath of disbelief, there was Josh Bailey, dead tired but somehow deciding he would stay on instead of changing, following the play and batting in the loose puck.

Then the initial eruption — followed by the third video review of the night from the blundering officiating crew led by Francois St. Laurent — and then the aftershock celebration. It was like that all night, as the first Islanders postseason since 2016, and first one that started on home ice since 1988, began with fireworks.

“It was a heck of a game,” Barzal said. “If the series is going to be like that, it’s going to be an enjoyable series for the fans, I’ll tell you that. It was a back-and-forth game, and it was fun to be a part of.”

The end of regulation itself was a study in heart health, as the Islanders’ 3-2 lead evaporated when Pittsburgh goalie Matt Murray was on the bench for the extra attacker and Justin Schultz got a shot through traffic and behind Robin Lehner to tie it, 3-3, with 1:29 remaining.

And before overtime could commence, it was Bailey, of all people, hitting the post with about five seconds hanging on the clock.

“That was tough to shake. I was worried I was going to have to see that one in my nightmares for a little while,” Bailey said. “A little bit of redemption — just happy to get the win. Crucial game, there’s still a long way to go. But good win for us.”

The Islanders’ surprising season was predicated on playing tight defense, and they got away from it in the second period when the Penguins power play was able to tie it on an Evgeni Malkin goal. Going into the third tied 2-2 with a team that has won three Stanley Cups in the past decade was not exactly ideal.

But just like they have all season, the Islanders didn’t budge. With a screen from Anthony Beauvillier, a floating Nick Leddy point shot beat Murray at 12:35 and gave the Isles that 3-2 lead.

“I liked our composure on the bench,” coach Barry Trotz said. “There were a lot of twists and turns in that game. Disallowed goals, and just a bunch of stuff. And we stayed with it. I liked our group, they didn’t flinch at all, which is good.

“In close games, we learned to be comfortable. And they’re going to be close games in the playoffs.”

Rest assured, one loss is not going to faze the Penguins. Just like they weren’t fazed with the Islanders’ game-opening goal from Jordan Eberle at 1:40 of the first period — that after a Tom Kuhnhackl goal at 33 seconds was pulled off the board due to a successful offside challenge from Pittsburgh coach Mike Sullivan. The Penguins answered with one from Phil Kessel at 5:42.

And then when Brock Nelson improbably scored for the Islanders previously woeful power play at 15:46 of the first, the Penguins answered later in the second on a power play of their own — and were kept at bay only by some brilliant saves from Lehner, who hardly backed away from his own NHL postseason debut as a starter, making 41 saves.

This is hardly the end to the high drama, with Game 2 back here on Friday night. That was only the opening scene in a script that is going to see just how far the Islanders can be pushed.

“That was completely different from the regular season,” Barzal said. “It was awesome.”