He came to camp in September 2016 as a nobody and today he’s the odds-on favorite to win the Calder Memorial Trophy.

How does an afterthought one year become an NHL rookie sensation the next?

On Tuesday night at Barclays Center against the Flyers, he led the Islanders to a 5-4 victory with two goals — including a spectacular late game-winner — and an assist.

He now totals 82 points (22 goals, 60 assists) as the third rookie in the club’s history to reach that mark and the first to do so in the NHL since Evgeni Malkin, who reached the mark in 2006-07.

Islanders 5, Flyers 4 Brendan Burke and Butch Goring break down all the action from the Islanders' 5-4 win over the Flyers in Brooklyn. Islanders 5, Flyers 4

His unmatched speed and scoring ability had the crowd roaring its approval when he converted the game-winner.

The wunderkind, Mathew Barzal, had the answer long before he signed on with the Islanders. Matter of fact, this was evident in a pre-draft interview in 2015 when a team’s rep candidly asked the center why he should be picked?

Barzal reportedly responded, “Don’t, and see how it works out for you.”

Matty later claimed the story was apocryphal but that doesn’t matter now, does it?

The Islanders obliged — selecting him in the 16th spot during the 2015 Entry Draft in Sunrise, Florida — and after a year of waiting, The Kid has made good on his alleged boast. And if it wasn’t a boast, he’s still made good — big-time.

Even with Arizona’s gifted Clayton Keller in pursuit (80 games: 23 goals, 41 assists, 64 points), all signs indicate that the 20-year-old Barzal will win the rookie-of-the-year award this spring.

[Watch Islanders-Rangers Thursday on MSG+2 & MSG GO. Download the app for free.]

“No question in my mind,” said MSG Networks analyst Butch Goring, “that Barzal will win the Calder. Other candidates may have had some good spurts but when you take Mat’s work from Day One, he’s done much more than the others.”

Butch Goring and Stan Fischler make their selections for their post-season award winners in the NHL.

Ironically, Barzal was a bust in 2016-17, playing only two games producing zero points, a minus-2 and six penalty minutes; including a premature playing-the-puck-before-fully-stepping-out-of-the-penalty-box miscue.

Nevertheless, when Mat showed up at training camp last September, The Sporting News waxed poetic about his future: “Poised and speedy, when the puck is on his stick. And he’s still refining the rest of his game.”

Coach Doug Weight felt likewise and at training camp last September, made it plain and simple in terms of Barzal’s future.

“If he earns it, he will play,” said Weight. “We want to win and I’ll take the players who earned that spot.”

Barzal earned it by dazzling with his skate work and a maturity that was lacking the first time around.

I vividly remember being in the MSG Networks interview room after our Shannon Hogan had given him the preseason Third Degree.

The earlier braggadocio was gone and even though he had been named the Western Hockey League’s playoff most valuable player of 2016-17, Mat knew that he had a heck of a lot to prove to management before making the varsity in October.

“When I was sent back to Juniors,” Barzal recalled, “I was frustrated. But then I put my work boots on and wanted to win a championship, and did that. I didn’t want to let a year go to waste and wanted to become a better player.”

That he accomplished the feat was evident last fall and during the first weeks of the season. The media critics, fans, teammates and management had to blink in amazement to be sure this was the same Mathew.

Super-motivated, he began piling up points; eventually pivoting a line with his youthful pal, Anthony Beauvillier, and veteran Jordan Eberle.

“His speed, skating agility and confidence all combined are what impressed me,” explained Eberle, who had come to the Islanders from Edmonton where he watched the amazing Connor McDavid excel. “Mathew can go a long way.”

Still, that was a bit premature. A month or two do not make a season. As Barzal improved, he became a target and had to prove he could handle the physical side of the game.

“He’s learning as he goes along,” said Weight, who worked with his prodigy as much as possible because the coach knew there was work to be done. “Yeah, he had to learn the defensive side of the game.”

As the weeks turned into the months of 2017-18, Mat captured the imagination of Brooklyn fans with his blend of speed, savvy and swirl.

“I’m amazed at some of the sudden moves he makes,” observed lineman Eberle. “His turns, his confidence are amazing for his age.”

The confidence became so apparent that the brash freshman soon was quarterbacking the power play because of his comprehensive ice view.

Meanwhile, the points piled up. An interview with The Sporting News stands out because it reveals his zeal.

“Why not be a player who can have the puck all night; play the most minutes, play on the first-line, the power-play and the penalty-kill?” Is the way the rookie put it.

Mark Parrish breaks down what makes Mat Barzal so effective for the Islanders and how he makes everything look so easy.

Most interesting is the fact that some of the best hockey minds — not to mention players — second the motion.

Toronto superstar, Auston Matthews, has watched Barzal play for years. And calls Mat “crafty, shifty and sharp on his edges.”

In a game against Matthews’ Maple Leafs on Feb. 22, Barzal’s club lost 4-3 in a shootout, but Mat produced three points (goal, two assists) and was a plus-three.

“Barzal makes guys around him better,” added Matthews. “He’s a fun player to watch — and a fun player to play against.”

Matthews’ teammate, defenseman Jake Gardiner, put it another way, “Barzal can really fly. He builds his speed up the ice coming 100 miles-per-hour.”

In a game against the Rangers on Jan. 13, Mat totaled five points on two goals and three assists in a 7-2 victory at Madison Square Garden.

“The first thing that stands out about him,” said Rangers defenseman Marc Staal, “is his speed and extreme quickness. He goes hard to the net and when he puts those things together he’s a really dangerous player.

When he’s out there, we all have to be aware of where he is at all times. Not just the defense but all five guys.”

The MSG Hockey Show Will Reeve, Anson Carter and Arda Ocal look at Mat Barzal's three-assist night against the Rangers and discuss whether or not the Isles have two superstars on their roster. The MSG Hockey Show

MSG Networks Islanders Play-by-Play man, Brendan Burke, has watched Barzal all season and calls his ability to process the game at high speed as Mat’s biggest asset.

“I put Barzal and Connor McDavid of Edmonton as the first two players who will be where the NHL is headed in 10 years. Right now they are the only two who have that similar skill set.”

After 80 games, he was averaging better than a point-per-game on 22 goals and 60 assists.

But none of this has happened accidentally.

Luke Fox of Sportsnet pointed out that Barzal has spent summers training with world champion ice dancer, Victor Kraatz, based in Vancouver near Barzal’s hometown, Coquitlam, British Columbia.

“I’ve really worked on my speed and edge work (with Kraatz) and gotten faster. That took my game to the next level,” said Barzal.

[Watch Islanders-Rangers Thursday on MSG+2 & MSG GO. Download the app for free.]

Others say the secret is in his crossovers. Teammate Cal Clutterbuck, one of the more insightful Islanders, offered this x-ray of Mat’s style:

“Once you give him room to make one or two crossovers, the race is over. It has a lot to do with his edges and how he uses them. The deception is, he doesn’t look like he’s really motoring that fast.

“He’s got that long, Mario Lemieux type of look-like-you’re-going-slow-but-you-blow-by-guys. His ability to change direction creates much space for him to get set up and make a play.”

Barzal: “Straight line, I don’t think I’m the fastest guy but when I can build some speed and get momentum that helps.”

After studying Barzal, Fox pointed out that Kraatz urged Mat to move his feet as fast as possible when crossing over. “Don’t worry about striding with power; try to increase the number of steps. Tuck four crossovers into a tour instead of three.”

Perhaps the most amazing aspect of all is that the Bruins had three chances to draft Barzal and passed on him each time.

After watching Barzal in several games, Devils radio analyst, Glenn (Chico) Resch believes the Islanders can build their franchise around Barzal.

“Mat reminds me of Taylor Hall of the Devils. I see energy, fun to watch — a joyful player who plays with fire. You watch Mat get the puck and then you say, ‘Oh, this is going to be fun to watch.'”

Mat Barzal reminisces about being coached by Devils' Taylor Hall and playing against a team coached by John Tavares when he was just 15 years old.

Not that Barzal is without flaws. His defensive work, as in backchecking, needs work. Too often, he holds on to the puck instead of shooting. But those are areas that can be remedied in time.

Most important are his basic skills and attitude.

“I love playing big games and that’s what makes it fun,” said Barzal.

The Kid has come a long way from the uncertainty of training camp. But the more his future teammates watched him, the more they realized that they were going to have a gem sparkle at center ice.

And unless all critics are wrong, he’ll be showing off his Calder Memorial Trophy next June.

[Watch Islanders-Rangers Thursday on MSG+2 & MSG GO. Download the app for free.]