Sean Strickland upset heavy pre-fight favourite Israel Adesanya to win the middleweight title at UFC 293 in Sydney, Australia.
American Strickland, 32, pressed forward relentlessly over five rounds, out-striking Nigeria-born New Zealander Adesanya to win a unanimous decision.
Strickland was only handed the title opportunity after an injury to fellow top contender Dricus du Plessis.
"Am I dreaming, am I going to wake up? Somebody hit me," said Strickland.
"Never in a million years did I think I would be here. I don't cry much but I'm trying to keep [myself] together right now."
Adesanya, 34, was originally set to face Du Plessis after facing off with the South African following his win over Robert Whittaker in July.
That fight did not come to fruition after Du Plessis was injured, forcing the UFC to consider other options.
With Adesanya already having beaten fellow top contenders Jared Cannonier and Marvin Vettori, the opportunity was handed to Strickland, who is fifth in the middleweight rankings.
Strickland came into the bout on the back of two wins, while Adesanya was making the first defence of his second title reign after emphatically beating long-term rival Alex Pereira in April.
Adesanya, competing in his 11th title fight, oozed confidence as he walked briskly to the octagon.
But, following an uneventful start to the first round, the odds started to even out as Strickland dropped Adesanya with a clean right hand, sparking the contest into life.
The champion recovered to reach the end of the round, but in knocking down Adesanya, Strickland laid down a marker that many of Adesanya's former opponents had failed to set.
Adesanya started to land more consistently in the second round, peppering the challenger with leg kicks, but Strickland, as he would for the remaining rounds, continued to be the aggressor.
And despite consistently pushing forward against a slick counter-striker in Adesanya, Strickland was able to avoid the majority of the champion's retaliations.
Halfway through the bout, Strickland's corner sensed their fighter could be on course for victory, asking for more urgency, adding "we didn't come all this way to lose a decision".
Strickland continued to press for the remainder of the fight, using his jab effectively, with Adesanya on the back foot and unable to inflict any meaningful damage in response.
As the fight ended, Strickland raised his arms in celebration, confident of victory, while a dejected-looking Adesanya walked over to his corner.
After the judges announced Strickland as the winner, Adesanya embraced the emotional American, before raising his hand in victory.
It meant Strickland won his maiden UFC title in his first championship bout, recording the 28th win of his 33-fight career.
"Izzy's had how many highlight knockouts, he's beaten the majority of my friends pretty easily. I was even doubting myself at times, but the fans in Australia motivated me," said Strickland.
"I give so many brain cells to the MMA gods every day. I thought I'd be walking away a little bloody and broken up, I'm still shocked that didn't happen, this is the first time I'm lost for words.
"But remember, this gold around my waist doesn't mean [anything]. What matters is how you live your life, and I'm living better through you guys, for you guys, thank you."
Volkov beats home favourite Tuivasa
In the co-main event, Russia's Alexander Volkov submitted Australia's Tai Tuivasa in the second round.
Tuivasa, 30, was aiming to halt a two-fight losing streak while the 34-year-old Volkov was looking for his third successive victory.
The heavy-hitting Tuivasa adopted a leg-kicking game plan against Volkov, who utilised his superior range to out-strike Tuivasa and stay out of danger.
As the fight went to the ground in round two, Volkov worked his way towards an advantageous position before securing an Ezekiel choke, forcing Tuivasa to submit.