If the Giants, or the rest of the NFL, knew then what they know now, Puka Nacua wouldn’t have fallen to the 177th pick and the fifth round and into the arms of Sean McVay’s Rams.

There were 19 receivers taken before him in the 2023 draft, including Giants third-round pick Jalin Hyatt, and Pacua has been the best of the lot, and he will take his Ram-Tough talents to MetLife Stadium on Sunday.

And he can’t wait to show New York what a phenom with a quiet chip on his shoulder looks like.

“I love the game of football, you’re gonna see my energy, I hope you get to see that I love this game of football,” Nacua told The Post by phone Thursday. “I’m gonna play super physical, I’m gonna play behind my pads and I’m gonna smile while I’m doing it. I’m gonna be smiling and dancing for sure.”

Nacua (96 catches, 1,327 yards, 5 TDs) is threatening the single-season rookie receiving yards record set in 1960 by Bill Groman (1,473 yards). Ja’Marr Chase (1,455) gave it a run in 2021.

“It doesn’t sound real,” Nacua said. “It doesn’t sound like that’s a question you should be asking me.”

Oh, it’s real. Nacua is even chasing C.J. Stroud for Offensive Rookie of the Year honors.

“He’s really taken the league by storm,” Deonte Banks told The Post. “He’s just a real good route-runner. And he got good hands. And he’s strong. He’s probably stronger than most people think.”

In a nutshell, Puka Nacua is a 22-year-old version of Cooper Kupp.

“They have the same skill set,” Giants DC Wink Martindale said. “They got great hands, they run great routes, they’re great run-after-catch guys. They’re physical when they block. It’s like having tight ends out there playing wide receivers, that’s how well they block.”

Nacua — 6-foot-2 and 205 pounds, 10 pounds heavier than Kupp — was fortunate to land with a creative genius like McVay and a quarterback on fire like Matthew Stafford and a mentor like Kupp.

“I think we’re both super-difficult to tackle after the catch. … Coop’s tempo change and his understanding of the game, in my eyes I wouldn’t say we’re too similar,” Nacua said, laughing.

Nacua had an injury-plagued career at Washington and BYU and ran a pedestrian 4.57 at his Pro Day. His game speed and his heart have made a mockery of the pre-draft process. He is a gamer.

“You could tell he was a smart, instinctive football player, and what they’ve done has been really impressive,” Giants OC Mike Kafka said. “He’s setting records as a rookie, and it’s awesome to see a guy like that.”

Not so awesome if you have to defend him.

“Big receiver, very physical, but I think besides his athleticism, what really stands out to me is his effort and how relentless he is,” Adoree’ Jackson said. “Plays all four quarters at the same speed. He reminds me a lot of [former Rams receiver] Robert Woods, who could go in there and block like the best of ’em, with the best of ’em. Can run routes with the best of ’em, and just has his attention to detail.”

Giants safety Jason Pinnock was a Jet when older brother Kai, a safety, was with Gang Green.

“It’s playing through the play. … It’s certain catches that other receivers or guys may even like kinda give up on,” Pinnock told The Post. “He tries for every ball, if it’s catchable, he’s gonna try. Kinda just that heart, really.”

The similarities to Kupp are noticeable.

“But he’s more of a deep threat too as well,” Pinnock said. “Obviously most of his are intermediate-to-catch-and-run style, but definitely I think a little bit more of a deep-ball threat than Kupp.”

Nacua is on the brink of passing Jaylen Waddle (104) and Anquan Boldin (101) for most catches by a rookie receiver.

“He can run, he’s got good catch radius, he runs good routes, and he got good YAC [yards after catch),” Xavier McKinney said. “He can make plays with the balls in space.”

Nacua (10 carries, 70 yards rushing) can run jet sweeps as well.

“A young man who took advantage of his opportunity,” Darnay Holmes told The Post. “A young man that had no sense of quit in him. When he got that moment, he seized it, and as a ballplayer, you gotta respect a guy like that.”

Holmes cited an example on film.

“A lot of guys catch an under route, get the first down and go down,” he said. “He’s not gonna go down.”

Nacua could not imagine that he would make this kind of immediate impact. Asked what he had proved to himself, he said:

“I guess that I could do it.”

Tyreek Hill was a fifth-rounder in Kansas City mostly because he brought domestic violence baggage into the NFL.

“You look at those things and you ask yourself ‘Why?’ It’s a funny science, the draft, so things like this happen,” Kafka said. “Thirty-one teams wish that something like Puka Nacua had happened to them.”