(THE GUARDIAN) - Daniel Cormier could hardly believe himself.

Sure, he was supremely confident he would get the job done. That is why, despite holding the Ultimate Fighting Championship's light heavyweight title, he moved up to challenge heavyweight champion Stipe Miocic.

But to dispense of the longest-reigning champion in the division's 25-year history in this fashion? Cormer paced around the octagon and kept muttering to himself, surely in shock of what he just accomplished.

A single, crushing right hand in the clinch laid Miocic flat on his back on Saturday (July 7) at T-Mobile Arena in Paradise, Nevada, before Cormier jumped on his foe, raining blows on his bloody face until the referee jumped in at 4:33 of the first round.

"I, ugh, I, ugh, I was a heavyweight a long time and I left the division," Cormier (21-1) said. "I never knew what I could become, but tonight I got the answer. I'm a two-division champion, baby!

"I am 39 years old, and I've been second a lot of times, but today I finally accomplish everything. From crying in this very same octagon almost a year age today…

"Listen to DC, there's a guy that I've know for an long time, he's a wrestler, he's an All-American, he's a former UFC champion. I never thought I would fight him, but Brock Lesnar, get your a** in here!"

Lesnar, who UFC president Dana White said will be returning to the organisation after a year-long banishment drug suspension incurred in 2016, stormed the octagon.

The two went nose-to-nose, setting up what is sure to be a megafight between the second man in UFC history to simultaneously hold titles in different weight classes and the crossover star, who held the UFC heavyweight title from 2008 to 2010 in between stints, while becoming one of World Wrestling Entertainment's biggest attractions.