Islam Makhachev beat home favourite and featherweight champion Alexander Volkanovski by unanimous decision to retain his lightweight title in an engaging contest at UFC 284 in Perth, Australia.
In a close contest, Russian Makhachev's counter striking and offensive wrestling gave him the edge over a gallant Volkanovski.
In victory, Makhachev 31, could replace Volkanovski, 34, who was attempting to become a double champion, as the UFC's pound-for-pound number one.
The bout was billed by the UFC as the first ever meeting between their current pound-for-pound number one in Volkanovski, and the number two-ranked fighter in Makhachev.
Volkanovski, who has dominated the featherweight division since winning the title in 2019, was stepping up to lightweight in the hope of following Conor McGregor, Amanda Nunes, Daniel Cormier and Henry Cejudo in becoming the fifth simultaneous double UFC champion.
Makhachev, meanwhile, was making the first defence of his title since beating Charles Oliveira at UFC 280 in October.
The Russian was a big pre-fight favourite with bookmakers because of his bigger size, with pundits pointing to his high-level wrestling as being the difference, but the fight was much closer than some predicted.
There was a party atmosphere as Volkanovski made his way to the octagon, voraciously cheered by the Australians inside the RAC Arena, while in contrast Makhachev sported a stern, focused look as he was booed during his walk-out.
Makhachev was also fighting without his coach, mentor and former UFC lightweight champion Khabib Nurmagomedov in his corner, after the latter suggested in January he was stepping away from the sport.
The fight begun with both athletes showing patience as Volkanovski feinted and switched stances, while Makhachev looked for openings.
Just over midway through the round, Makhachev had his first significant moment as a punch stunned Volkanovski, illustrating the difference in power, before he landed a takedown and ended the round in a dominant position.
The key moment in the second round belonged to Volkanovski however, as following another takedown from Makhachev, he managed to achieve what many previous opponents have struggled to do and got back to his feet.
Volkanovski's resilience spurred the Perth crowd on as they roared with every punching combination and leg kick he landed through the next few rounds.
Makhachev continued to use his range to his advantage, countering Volkanovski with swift left hands and takedown attempts.
Following a dominant fourth round on the ground for Makhachev, Volkanovski pushed forward in the fifth, perhaps knowing he needed to convincingly win the round to secure victory.
After showing strong takedown defence, Volkanovski dropped Makhachev towards the end and finished the fight in a dominant position, pounding him on the canvas.
As the bell rang, both fighters got up and raised their arms, confident of victory, with everyone at the side of the octagon on their feet applauding both fighters' displays.
The result meant Makhachev ended Volkanovski's 12-fight UFC winning streak and extended his own to 12, which is now the current longest in the promotion.
"I thought he was going to be easy on the ground but this guy proved he wasn't," said Makhachev.
"I showed why I am number one. If you like it, I am the best fighter in the world right now, thank you."
Volkanovski meanwhile, paid tribute to his opponent.
"I appreciate the support but let's have a round of applause for Islam. Obviously a lot of people are going to be happy with that because they didn't give me a chance but it was a fun fight," he said.
"Obviously I'd like to say this message with a win but there's nothing wrong with challenging yourself. Challenge yourself like this it only makers you stronger.
"You can see I can get the job done but I came up short tonight, congrats to Islam, great fighter."
In the co-main event, Mexico's Yair Rodriguez put on a fine performance as he beat American Josh Emmett for the interim featherweight title via a second-round triangle choke.
Rodriguez, 30, mixed up his striking beautifully, landing an array of damaging kicks, punch combinations and elbows.
Emmett's power shone when he struck the elusive Rodriguez, but he was second best throughout.
When the fight went to the ground, Rodriguez showed another layer to his dangerous set of skills as he locked in a triangle choke to end the fight.
Rodriguez's win will likely set up an undisputed title fight with Volkanovski, who has said he wants to stay active in both the lightweight and featherweight divisions.
