Nikita Tszyu in TKO win on huge day for boxing family

He may be living in the shadows of his world-champion brother, but Nikita Tszyu maintained his own unbeaten professional record with an emphatic TKO victory on a triumphant and historic day for Australian boxing's most successful family.

The 26-year-old emerging star floored countryman Bo Belbin early in the fourth round with a heavy left before the referee stopped the fight half a minute later following another flurry of head shots from the so-called "Butcher".

Belbin was already sporting a bloodied nose and a nasty cut under his left eye after suffering a battering in round three.

Having already taken down Ben Horn, the younger brother of former WBO welterweight champion Jeff Horn, Tszyu stopped short of calling this his best win yet.

But he was mightily satisfied at snapping Belbin's own unbeaten record in the Tasmanian's eighth fight.

"I'm proud of it. I stayed composed during some tough times in that fight," he said.

"He caught me early but I stuck to my game plan. We're like brothers in a way - with the same mindset - and I truly respect him."

Tszyu's latest super-welterweight victory improved his record to 5-0, with four knockouts.

Sunday's bout at Sydney's Qudos Bank Arena also marked the first time Tszyu and his superstar brother Tim fought on the same card.

Tim ensured it was a day of celebration with a ninth-round knockout of American Tony Harrison to capture the interim WBO super-welterweight title and join his legendary father Kostya as a world championship winner.

With so much at stake for his big brother, Nikita said winning the precursor felt non-negotiable.

"If I had lost the first fight, that would have been a horrible headspace for Tim," Nikita said.

"I knew there was no other way besides victory for this. That stayed in my mind the whole time."

In the co-main event, Paulo Aokuso plundered and played with Yunieski Gonzalez (21-6, 17KO), winning comfortably on points to move to 4-0, all KOs, and claim the vacant IBO Inter-Continental light-heavyweight title.

Aokuso has his sights set on beating compatriot Jeff Fenech's national record by nabbing a world title in just six professional fights.

But, despite dropping the veteran Cuban midway through the 10-round tussle, the Australian Olympian was denied the showtime stoppage that would have helped his cause.

In another feature bout on the undercard, classy Sam Goodman (14-0, 7KO) retained his IBF Inter-Continental and WBO Oriental super bantamweight titles with a unanimous points win over Ireland's Sydney-based former world champion TJ Doheny (23-4, 17KO).

And Rohan Murdoch (27-2, 19KO) won a split decision over a livid Issac Hardman (13-2, 11KO) to claim the IBF Australasian super-middleweight title.