Anthony Beauvillier of the Islanders celebrates his overtime goal against...

Anthony Beauvillier of the Islanders celebrates his overtime goal against the Buffalo Sabres with teammate Brock Nelson at NYCB Live's Nassau Coliseum on Saturday, Dec. 14. Credit: Jim McIsaac

Anthony Beauvillier is only 22 and presumably in better shape than you or me, but he had an exhausting day at the office on Saturday.

Fifteen minutes after punching out from his final shift he still was breathing so hard he struggled to speak.

Was this sort of thing unusual for him? “Yeah, yeah it is,” the Islanders winger said. “I usually recover really fast. I just had a tough time today.”

He said he “kind of felt heavy” and that “it seemed I couldn’t really find my breath,” citing the 1 p.m. start as a possible reason.

But it didn’t look like a tough day from afar. He set up the first goal, got a secondary assist on the second and scored the third, 3:04 into overtime for a 3-2 victory over the Sabres at NYCB Live’s Nassau Coliseum.

That last one is when the out-of-breath thing came into play. Beauvillier was not sure he had it in him.

It had been an eventful overtime already. He was fortunate not to get called for interfering with Sabres goaltender Linus Ullmark.

Then he tried to check Sabres star Jack Eichel, who is 6-2 and 203 pounds, in the offensive zone, bounced off him, landed on the ice and handed Buffalo a gift 3-and-2 rush. Doom seemed imminent.

But Brock Nelson tipped Eichel’s attempted cross-ice pass, and the puck found its way to Beauvillier, who by that time had made his way back to the far blue line.

With what he later said was the last bit of energy left in him, he gathered the puck, scooted down the ice and beat Ullmark for the winner.

“He did a good move; he’s a great player,” Beauvillier said of Eichel. “I thought I had him on the check there. I found some legs, I guess, on the way to the breakaway.”

Beauvillier said he was so gassed that when teammates were putting their gloves in his face during the victory celebration, he thought he was going to pass out.

The important news for the Islanders is that his big day was not a one-time thing. Now in his fourth season, the former first-round draft pick has rounded into a complete, consistent player.

He has 10 goals (third-most on the team) and 21 points (fourth-most) and has developed enviable chemistry with centerman Brock Nelson.

“I think he’s playing with confidence,” Nelson said. “His speed is one of his greatest assets. He‘s good with the puck in tight spaces. He can make you pay.

“He doesn’t need much space, and when he gets his chances, he’s been burying them this year. That’s added to the confidence.”

Beauvillier had 18 goals and 28 points last season but endured some dry patches. Coach Barry Trotz said learning to play through those has paid dividends.

“If you remember last year, I thought Beau went 20 or 21 games with really no production,” Trotz said. “I let him try to work through it as a young player, didn’t take him out of the lineup when he wasn’t producing.

“I kept talking to him and showing him stuff and letting him try to figure it out, and I think he did.”

Beauvillier said the change mostly has been psychological.

“Just my mindset,” he said. “I’m still the same player. I have the same speed, same ability to make plays, same shot. It’s just in my head I think I’m more confident. I know I can make plays. I know I can be a factor.”

If he can keep it up, it will be a huge bonus for a team that relies on balance in the absence of an elite, goal-scoring sniper. Its best player, Mathew Barzal, still is a playmaker at heart.

On Saturday, Beauvillier was the clutch scorer the Islanders needed on an afternoon that took his breath away.

“I guess,” he said, “I found an extra layer of legs there at the end.”