Usyk, a former Olympic gold medallist, holds all major titles after just 15 professional fights — the majority of which he travelled abroad to take on rivals in their own backyard.
"Moscow, 2018. Bang! Daddy's in the building," Usyk said.
Usyk added he could move up to heavyweight to fight the experienced British fighter Tony Bellow.
He called out the British star straight after his victory — putting the entire heavyweight division on notice.
"If he doesn't want to drop down (to cruiserweight), I'll happily go up to meet him," Usyk said.
"I'll just eat extra pasta."
It was Usyk's third fight in 10 months as part of the World Boxing Super Series, in which he also beat German Marco Huck and the then-WBC champion Mairis Briedis.
Gassiev's record dropped to 26-1 with one no contest.
"I had the best opponent in my professional career," Gassiev said.
"I do my best, just today is Oleksandr's day."
It certainly was.
According to many fight commentators, Usyk didn't lose a single round against his champion opponet.
The most terrifying feature of his victory was that his most aggressive round was the 12th and final round, where he landed 47 strikes and threw 117 — despite already being unable to lose the fight on the judges' scorecards heading into the final round.
The performance makes him as a future superstar, according to many commentators.
Usyk was born in Crimea and has said he was forced to leave the peninsula after Russia annexed it from Ukraine in 2014.
Despite the tension between the two countries, Usyk and Gassiev embraced warmly after the fight with broad smiles.
On the undercard, Cecilia Braekhus remained the undisputed women's welterweight champion after beating the relatively inexperienced Russian Inna Sagaydakovskaya by unanimous decision.
The Norwegian, who first won a world title in 2009, has a 34-0 record.
news.com.au/AP
