To know what brought this moment into existence, and what brought this player into ascension, let us go back to a living room in Oakville, Ontario.

It’s 1995, and a 5-year-old John Tavares puts on a tape of Wayne Gretzky highlights, watching from start to finish for almost an hour. It’s over, he rewinds, and he plays it again.

Tavares’ mother, Barb, takes her young son across the border to Buffalo, where her brother-in-law, also named John Tavares, is playing indoor lacrosse for the Buffalo Bandits. Little Johnny sat rapt, not getting up to run around, not interested in ice cream. From start to finish he watched his uncle play, absorbing it all.

“He’s definitely more than a hockey player,” uncle John told The Post over the phone Monday from his Canadian home, hardly needing to be the leader of the band beating the drum for Tavares as New York’s leading athlete as this spring inches toward summer.

That’s because on Sunday night in Brooklyn, Tavares did that for himself with a moment that will live forever in this town’s sporting lore.

Tavares is now the 25-year-old captain of the Islanders, and if you could take your eyes off him at any time he touched the ice during his team’s first-round series against the Panthers, you were missing something special. But for all of his heroics, nothing compared to this transcendent, one-man effort — getting the rebound of his own shot, wrapping around the net, reaching out and scoring on a backhand. The goal ended the game in double-overtime, ended the Islanders’ 23-year streak of playoff futility without winning a series, and put his face where it rightfully belongs, next to the greats in New York sports.

“The puck came through to me,” Tavares said on the ice afterward, “and it’s funny how things work sometimes.”

That moment came at the end of a six-game performance from Tavares that has put him at the top of the very early list of Conn Smythe favorites as postseason MVP, with his team preparing for a second-round matchup with the Lightning that starts Wednesday night. But with the Isles trailing 1-0 to the Panthers in Game 6 and less than a minute remaining in regulation, it looked like a trip back to Florida for an unpredictable Game 7 was imminent. Ghosts of Islanders postseasons past hung over the new rink at Barclays Center and teased the fans into a silent gloom.

But Tavares charged the net and buried a loose puck, tying the game and forcing those nail-biting overtimes, setting the stage for the grand finale of his monumental series. Because it had been more than just one game for No. 91 in blue and orange. He scored five goals and added four assists in the six games, contributing on nine of his team’s 15 goals in the series.

The Islanders haven’t shown a ton of depth up front, and Tavares has a left winger named Alan Quine, who made his NHL debut in the second-to-last game of the season. But everyone on this team has become the supporting cast to the main attraction. Which is always the way it has been for Tavares.

“He’s had the spotlight on him for a long time,” Tavares’ uncle said. “I think that makes it even more impressive. Not only is he on the biggest stage possible right now, but he’s been for a long time. It’s a lot of pressure to perform, and he’s done nothing but get better over the years.”

Growing up playing a lot of lacrosse, some soccer and even a bit of basketball, Tavares wasn’t fully swallowed by the hockey world until his early teens. But by then, it was obvious he was so much different than the rest of the kids around him.

“I have my son now, he’s 10 years old — he’s average at best,” said uncle John, who is arguably the best indoor lacrosse player of all time, just retiring last year at the age of 46 after 24 seasons. “I remember watching John at approximately the same age, and John was one of the top players at his age, if not the age above as well. You never want to tell other people or think, ‘Wow, this kid is special, he’s going to The Show.’ You don’t want to be that guy. Because there are so many variables, you don’t know what’s going to happen, how they’re going to mature, if other kids are going to catch up to them.

“But obviously John had a knack for scoring and playing hockey at an early age. And he’s got a very good head on his shoulders.”

Tavares was so good as a 14-year-old that one of the three best junior leagues in the world, the OHL, amended its rule for age limits and allowed him to enter the draft with “exceptional player status.” It’s been adopted across all Canadian Junior leagues, and is known as the John Tavares Rule.

By the time he was 17, Tavares was trying to get his way into the NHL draft, but the league wouldn’t break its own age limit. After dominating the OHL for three seasons, he was allowed to enter the 2009 NHL Draft as a 19-year-old, and the Islanders took him with the No. 1-overall selection. He never spent a day in the AHL, and his only experience in professional hockey has been as the hopeful savior for a previously proud franchise fallen on moribund times.

“When we drafted John, we knew he was a world-class talent, had an excellent compete level and off-the-charts character traits,” general manager Garth Snow told The Post via text. “He has been nothing short of sensational in all of those areas for our team and our organization.”

It’s hardly been all roses and rainbows for Tavares or the Islanders. Those early years of his career were so often played at a half-empty Nassau Coliseum as the place crumbled around them, and the team lost over and over again. An individual fire can only burn bright if there is air around it to breathe.

Still, Tavares showed faith. He signed a six-year, $33 million deal beginning in 2012 that has two years remaining with a modest annual salary-cap hit of $5.5 million.

They finally broke a five-year playoff drought in 2013, when Tavares used the lockout-shortened season to collect the first of two nods as a finalist for the Hart Trophy as league MVP. But the good vibes were short-lived when his team lost in the first round to the top-seeded Penguins. After missing the postseason in 2014, the Isles made it again last year but were an absolute no-show in Game 7 of the first round against the Capitals.

Now it’s the first year with the franchise calling Kings County its home, and it hasn’t been the smoothest transition. As recently as March 21, they had just lost 4-1 to the Flyers and were 0-3-1 in their previous four games, with Tavares without a goal in five straight. Their postseason berth was beginning to be put into question.

“It’s an important time of year, we’re not playing our best, and it starts with myself and leading the way,” Tavares said that night. “I know I have to be better.”

Pointing the finger at himself is something he has always done, going back a long way.

“That is in John’s character,” his uncle said. “He’s the captain of that team. He wants that pressure. He wants that puck. He wants as much ice time as possible. He wants to be given the opportunity to perform for his team. So if the team’s not doing well, the first guy he’s going to point at is himself.

“When you have a leader that points the finger at himself, guys look at that and go, ‘You know, I want to work hard for that guy.’ ”

There never has been a question about how good Tavares is, or how good he could be. The only question has been if he could be part of a team that was just good enough, so he could carry it to the promised land.

So now the Islanders are firmly strapped to his back, and how far he can take them will be fascinating to watch over the next few weeks. But one thing that already has been established is that for as long as Tavares is playing, taking your eyes off him means you’re missing the best show in town.