It's a new era for the UFC and the sport of mixed martial arts.
So what's at stake in the UFC's first main event on ESPN airwaves? Here's everything you need to know, Cheat Sheet style.
Henry Cejudo (13-2) vs. TJ Dillashaw (16-3), flyweight championship
The first question everyone asked when the UFC first announced that TJ Dillashaw would drop from 135 pounds to challenge Henry Cejudo at 125 was a simple "why?"
Why make this at flyweight? It's no secret the UFC is considering eliminating the division altogether. It already has released several flyweights from their contracts and parted ways with the longtime face of the division, Demetrious Johnson.
Why not have Cejudo, who won the title by defeating Johnson in August, move up?
The answer has to do with ongoing contract negotiations between Cejudo and the UFC -- and Dillashaw's desire to chase a second belt.
Cejudo, who also is an Olympic gold medalist in wrestling, initially wanted to move up, but he admitted "negotiations didn't go as I wanted" with the UFC. As a result, Cejudo opted to defend his belt -- and in doing so, preserve the flyweight division, for the time being.
That decision put the ball in Dillashaw's court, and it was an easy decision for him to move down. Dillashaw already had offered to do so in 2018.
"No one wants to do this because it's a lot of work," Dillashaw said. "I worked my butt off, literally, to get this opportunity.
"The long-term goal is to leave this sport as the greatest ever. Doing things no one has done, eventually win three belts. I know I can be a 125-pound champion, and I know I can move to 145 and beat [defending champion] Max Holloway. I'm not looking past Henry, but I'm using him as a stepping stone to that."
It has all made for a unique title situation, with added stakes on both sides:
For Cejudo, who is coming off a win against arguably the No. 1 pound-for-pound fighter at the time in Johnson, it's a bet on himself and a potential life raft to the flyweight division. (UFC president Dana White has not committed to what will happen past Saturday.) And for Dillashaw, it's about building a legacy.
It obviously takes a well-rounded performance to upset the most dominant champion in UFC history -- as Cejudo did in August -- but what stood out most in that performance was Cejudo's counterstriking.
He pursued Johnson against the fence here and there, but he really got off his most effective work when Johnson was coming to him. And that's impressive, given Johnson's feints, defense and speed. He's just not easy to counter.
Cejudo always has the option of moving forward, as he has no fear of being taken down, but it would not be surprising if he planted his feet and looked to counter again. Dillashaw is unorthodox and unpredictable, but he also takes risks and is so offensively focused that he can leave openings for return fire.
Dillashaw's kicks could be a difference-maker. He's comfortable at long range, and remember, it was a head kick that turned the tide in his first win against Cody Garbrandt in 2017. Kicks are probably an underrated aspect of Dillashaw's game.
Of course, there is an Olympic wrestler in the Octagon here, and that is likely to come into play at some point. Dillashaw won't be outmatched in the clinch, but it seems doubtful he'll look to fight there. Cejudo's adjustments and takedowns from the clinch were another aspect of his win against Johnson that stood out.
Prediction: Dillashaw via third-round TKO