There’s a reason why they call it the “pivotal Game 5.” And it was only fitting that one of the tightest series of the first round needed double overtime to decide it.

Josh Bailey was the hero for the Islanders, scoring 51 seconds into the second extra period to secure a 3-2 win over the Penguins at PPG Paints Arena on Monday night. The victory gave the Islanders a 3-2 series lead and sets them up with a chance to advance as they head back to Long Island for Game 6 on Wednesday.

One team was going to come out of Game 5 with its backs against the wall, and the Islanders just barely escaped being that team.

Despite dictating play for a majority of the game, the Penguins fell short after netminder Tristan Jarry’s failed clearing attempt was scooped up by Bailey and carried in for the soft shot from between the circles for the game-winner.

“I just said, ‘Listen, dig in, play the right way, and there’s not a bad shot,’ ” head coach Barry Trotz said of his message to the team in between the first and second overtimes. “Keep the shifts short, be on the right side of the puck and it’s going to be all about who wants it more. I know you’re tired, but stick with it, this is about character and care for each other.

“Nothing’s easy in this league, it’s hard, and this is a hard division. This is a very good hockey team that we’re playing. It’s gonna take every ounce we have of everything we have to win this.”

The Islanders’ sense of urgency didn’t come through until the third period, when they were trailing 2-1. They didn’t record their first shot of that period until 8:50, but it happened to go in. Jean-Gabriel Pageau forced a turnover in the corner with a hit before Leo Komarov dished to Jordan Eberle, who lured Jarry out of the crease before burying it to knot the game 2-2.

It revitalized the Isles, but shortly after, Oliver Wahlstrom had to be helped to the locker room after falling awkwardly to the ice following a hit from Penguins defenseman Michael Matheson.

The Islanders had just 19 shot attempts through two periods, bowing to the Penguins’ speed particularly in the second period, getting outshot 20-4 on the way to a 50-28 disadvantage in attempts. Despite having some offensive-zone time, including a power play, the Islanders struggled to put the puck on net but the Penguins only came away with a 2-1 lead.

That the game was that tight could be chalked up to the play of goalie Ilya Sorokin, who finished with an Islanders rookie playoff record 48 saves on 50 shots, including nine in overtime. If not for the individual efforts of Sorokin and Anthony Beauvillier, who willed himself to the net with a swift move around Penguins top-line winger Jake Guentzel to tie the game 1-1 with 54.4 seconds left in the opening frame, the first two periods could’ve been game-defining.

“It was big for us,” Beauvillier said of his goal, “But we couldn’t have done it without Ilya, he kept us in the game.”

The team which has scored first had won the series’ first four games, but that trend ended in Game 5. The Islanders’ shaky play through a majority of regulation nearly kept that streak alive. They can thank their lucky stars for this one, and their names are Sorokin and Bailey.

“There’s one thing I know about this group of guys, we left it all out there,” Pageau said. “Just to get rewarded, might not have been our prettiest one, but to leave it all out there and to get rewarded for our work. Just to stick with it, is just an amazing feeling. We got to turn the page, we’re definitely happy about this one. But we got to really focus on that next one.”