Sonny Bill Williams has knocked out Barry Hall inside two minutes and says Paul Gallen could be his next opponent.

New Zealand's dual-code football star Williams demolished the AFL great in Sydney on Wednesday night, dominating from the opening seconds.

Williams jolted Hall in the first 30 seconds with some crisp, accurate shots.

Hall was down after just 47 seconds, though referee Les Fear said he did not see a punch and said it was not a knockdown.

Within 40 seconds, Hall returned to the canvas after taking a couple of big shots.

A ruthless Williams ended the contest a few seconds later, after he landed a big right hand that felled Hall, prompting Fear to end the one-sided contest after one minute and 55 seconds.

The 36-year-old Williams, who weighed in 11 kilograms heavier than Hall, improved his professional record to 9-0 while Hall dropped to 0-1-1.

"There's a reason why only one per cent of people do this type of stuff. So much respect for Barry and his team for coming in and doing this," Williams said.

"Because I was nervous before the fight."

Asked about his next fight, Williams referred to the long-talked-about match-up against fellow former NRL great Gallen.

"There's talk of Gallen, so maybe Gallen," he said.

Another winner on the undercard was professional debutant Rahim Mundine, the third generation of the outstanding Australian boxing family.

With both father Anthony and grandfather Tony in his corner offering advice, light heavyweight Rahim scored a unanimous four-round points win over Fijian Lepani Levatia.

Mundine displayed some of the traits of his father, utilising slick feints and sometimes carrying his hands low. He looked relaxed and composed and fired off some slick flurries of blows.

AAP