Islam Makhachev knocked out Alexander Volkanovski in the first round to retain his lightweight title at UFC 294 in Abu Dhabi.
Russia's Makhachev, 31, dropped Volkanovski, 35, with a left high kick, causing the referee to stop the fight.
The win concludes the pair's rivalry after Makhachev's narrow win in February.
It also all but ends Australian featherweight champion Volkanovski's hopes of winning a second title.
Volkanovski took the fight against Makhachev on 12 days' notice after Brazil's Charles Oliveria pulled out injured.
"Thank you to Volkanovski. You have to turn out the lights to beat this guy," said Makhachev.
"He will never give up. He will fight all five rounds, he is a real champion."
In the middleweight co-main event, Khamzat Chimaev beat Kamaru Usman by majority decision in a compelling contest.
Chechen-born Chimaev got the better of the grappling exchanges between the pair and is now in prime position to challenge middleweight champion Sean Strickland for the title.
In his post-fight interview, Chimaev, along with a number of others fighters, called for peace and an end to the violence in the Israel-Gaza war.
ncG1vNJzZmivp6x7o67CZ5qopV%2BovbC%2B02ikorCVmXqurdGtoJqkXZa%2Ftb%2BOb25qcGRnhnI%3D