TMZ Sports talked to the 21-year-old, 1-0 boxer ringside following the Fury-Deontay Wilder trilogy fight ... and we asked him how Fury would've fared against his legendary grandfather.

"That would be my favorite fight to watch. That would be the greatest fight of all time. The press conferences would sell out, the weigh-ins would sell out. The fight would sell itself," Ali Walsh said.

Okay, okay ... this obviously is nothing more than a fantasy matchup, a dream fight ... but it's fun to imagine.

Picture Fury and Ali -- 2 of the best talkers the sport has ever seen -- on the mic before the fight. Then, once in the ring ... wow.

We also asked Nico where Fury ranks all-time ... and it's clear how highly the young fighter thinks of the Gypsy King.

"I’ve always said that Tyson Fury is the greatest Heavyweight of my era, and I gotta say that Deontay is number two. And that's what Tyson said. It was an amazing fight tonight."

But, where does Tyson rank all-time?

"I’d put him in the top five heavyweights of all-time. He’s unlike any other heavyweight." Ali Walsh told us.

And, who'd win that fantasy matchup between Fury and Ali?

Well, Nico has an idea ... but even he admits he might not be the most objective her.

"I'm biased, but I'd say my grandfather all the way."