Israel Adesanya declared "there is no one like me" and said if he could sing even Justin Bieber would not have a job after dethroning middleweight champion Robert Whittaker in front of a record-breaking Melbourne crowd at UFC 243.

Interim champion Adesanya scored a stunning second-round knockout at Marvel Stadium, where 57,127 fans were in attendance, to become the undisputed champion in the division.

Australian Whittaker had already been floored by a huge right hook late in the first round and a stinging left in the second brought an end to the bout.

Adesanya made a grandstand entrance with a choreographed dance routine and the Nigeria-born New Zealander said his confident arrival was something he had planned to do in the past.

"I tried to do that in the Anderson Silva fight in February and the UFC were like, 'no, we can't have that'," he said.

"This fight is my show. I'm headlining this b****, so I was going to do it my way.

"Who else, on this kind of stage, is going to do that before they go in and whoop some ass? If I could sing, trust me - Justin Bieber wouldn't even have a job." 

Adesanya had no doubts he would pull off the victory, but confessed the gravitas of his achievement was still sinking in.

"It feels like I'm still lucid dreaming," added the 30-year-old. "You might see me do weird things, just to see if I'm dreaming.

"I said it was one my toughest tests, but that I'd make it look easy. I told you guys that.

"When I saw him walk out, he was too intense. You can't fake that s***, pull the hoodie over your eyes.

"I can smell it off him, that he wasn't with it. He was doing the right moves, but there was no feeling behind it.

"I saw everything coming. He hit me a few times, but I just showed that I can take and give it as well."

Whittaker had won his previous nine fights and vowed to rebound from the setback.

"Hats off to Adesanya, a great striker," he said. 

"I felt I was doing pretty well until you get caught. I'm only 28. I've still got a fight or two yet. I'm not going anywhere."