"Bro, it's another level. We get to fight on a historic event by a promotion that's already known for making history. So it's an honor to be chosen to go in there, a featured fight and kind of kick off the night for both co-main and main event," T-City told TMZ Sports earlier this week, just days before his clash with 29-year-old Diego Lopes.

Remember, Ortega, 33, and Lopes were supposed to fight in June at UFC 303 ... but the fight was scrapped the same day the men were due in the Octagon after Brian, who was coming off a win over Yair Rodriguez, got sick and couldn't fight.

Diego ended up accepting a new opponent, Dan Ige, on just several hours' notice. Despite Ige being fearless, Lopes won by unanimous decision.

FWIW, Ortega told us he had "respect" for both men, and what they did that late-June night.

Now, months later,  the originally scheduled fight is finally about to happen ... and it'll come directly before the two title fights -- main event, Sean O'Malley vs. Merab Dvalishvili and co-main, Alexa Grasso vs. Valentina Shevchenko.

We talked to Dana White earlier in the week ... and the UFC boss confirmed this would be the only event at the Sphere, as the promotion has a deal with MGM. Not to mention, they've sunk $20 million into the event.

Of course, September 14 isn't just any ordinary day. The event has been made around Mexican Independence Day -- commemorating the start of Mexico's fight to get out from underneath Spanish rule in 1810 -- with many Mexican or Mexican-American fighters making up the card.

Mexicans have a proud, rich history in the sport of boxing, and Ortega says they're just now beginning to make their mark in MMA.

"You've seen Mexican boxers your entire life, and you saw the wars and the show that it left behind for you guys. Well, these Mexicans are now here in MMA, where there is another level of excitement. The entire night is on Mexican Independence Day, on a historic event where every single person is going to be trying to make a statement for the history books."