Dana White and the UFC are hosting one of their most ambitious cards ever at the Sphere on Saturday -- and that's saying something for a guy who built an entire "Fight Island" -- an event the UFC honcho tells us wouldn't be happening without Tom Brady!

White joined Babcock on TMZ Sports TV show (airs nightly on FS1) this week ... where he revealed TB12 was the inspo behind the first-ever Sphere sporting event.

"I went to the Sphere with Tom Brady. He invited me to come to U2 with him. Had Brady not invited me, I wouldn't even have been to the Sphere yet. It's almost like this was meant to be," the UFC CEO said of the mega event.

FYI, the Sphere is a state-of-the-art venue in Las Vegas that offers an incredibly unique, immersive viewing experience unlike anything the world has ever seen.

In fact, White says his fight promotion is under contract with MGM, and if not for a dispute, UFC 306 almost certainly would've gone down at T-Mobile Arena -- which is owned in part by the casino giant.

"No matter how it plays out, this was supposed to happen. It's a one-and-done. I'm under contract with [MGM] and I'll be back with [them] after this event."

If you haven't heard about Saturday's UFC 306 card, AKA Noche UFC -- which comes on Mexican Independence Day weekend -- it goes down September 14 in Sin City ... and features two title fights, including a matchup pitting "Suga" Sean O'Malley vs. Merab Dvalishvili.

Dana says the ultimate goal was to celebrate the Mexican heritage ... and what the people have brought to the world of fighting.

"I call it my love letter to the Mexican people on Mexican Independence Day. We're going to talk about their traditions, their culture, their history, and their contributions to combat sports," White told us.

Doing all that wasn't cheap ... but Dana says it looks like the promotion is in for a historic night.

"I'm 20 million into this thing but pre-buys, we've had the biggest pre-buys ever in UFC history for any event we've ever done. And the gate's looking like it's going to be $23 million, which is the biggest gate we've ever done."

Check out the full interview with Dana ... he gets into what viewers at home can expect from the event, and he also previews a few of the fights he's most excited about.