Paul Vs. Diaz Was As Big As Mayweather Vs. McGregor, Says Shawn Porter

Jake Paul's fight against Nate Diaz was on the same level as one of the most popular fights in combat sports history -- so says former boxing champ Shawn Porter, who tells TMZ Sports Saturday's event felt "just as big as" Floyd Mayweather vs. Conor McGregor!

Porter -- who was on the mic in Dallas for the big matchup -- said the vibes were off the charts throughout the Jake vs. Nate fight ... calling the experience Super Bowl-esque.

"This was just as big as Mayweather and McGregor," Porter emphatically told us on Monday.

FYI -- Floyd vs. Conor is widely reported as the second-highest-selling fight in Pay-Per-View history (behind Floyd vs. Manny Pacquiao) ... so to compare the energy at Jake vs. Nate to that is quite a compliment.

Of course, "Showtime" is no stranger to the biggest events in the sport -- whether he competed in or attended them, he's witnessed some electric crowds over the years.

But Porter said the spectator support of Diaz was second to none ... adding, "I've never heard anything like that before."

"MMA fans, man. They show up, they show out, they have a lot of fun and they are extremely loud. I was loving it."

As for the fight, Shawn gave Jake a C grade on the night, despite getting the victory ... explaining the Problem Child still has to work on finishing off his opponents after landing big punches.