Tim Tszyu and Errol Spence Jr will fittingly slug it out at exactly the same weight in an intriguing blockbuster where no one can predict the outcome.

Tszyu (27-3, 18KOs) and Spence (28-1, 22KOs) both hit the scales at 159 pounds (72.1kg) at Saturday's weigh-in, as Australia's home hope places his career on the line in Sydney.

'A lifetime of work and I thank you, Australia, each and every one of you guys. Let's do it,' Tszyu said ahead of the boom-or-bust showdown at Afterpay Arena on Sunday.

'Let's do it for this country, man.'

After three shattering world-title defeats in the USA and defending his family's incredible 55-0 unbeaten record in Australia, the former WBO world super-welterweight champion knows his career could be over if he loses again.

But the 31-year-old isn't entertaining any such prospect.

'Look, why would I go into a fight if I think I'm going to lose? It doesn't work like that,' Tszyu said.

'We're all warriors. We've got something in here (our head) that makes us tick.'

With the American superstar's only ever loss coming against undefeated pound-for-pound legend Terence Crawford, Spence is also risking tarnishing one of boxing's great legacies.

'Pressure is something you create in your mind. It's a mentality. I don't have any pressure on me,' Spence said.

'Pressure is people not having food to eat. That's pressure. This ain't no pressure. This ain't going to make me as a guy, fighting another man.

'I thank everybody for coming out, and there's nothing more to say. It's fight time. I'm ready to go.'

While Tszyu and Spence are ready to punch on in one of the biggest bouts in Australian boxing history, the luckless Liam Wilson has been dealt another cruel blow, with his scheduled world title eliminator against Stephen Fulton cancelled after the American failed to make weight.

In farcical scenes, Fulton hit the scales at 139.5 pounds on Saturday, almost 10 pounds more than the two-division world champ was originally supposed to fight Wilson at in Sydney.

Fulton and Wilson were supposed to square off at the super-featherweight of 130 pounds before officials on Friday raised the weight to 133 pounds for the feature bout on the Tszyu-Spence card.

Wilson had happily agreed to the late allowance, saying he was desperate to earn another world title shot with a victory over the former unified super-bantamweight world champion and ex-WBC featherweight belt holder.

But Team Fulton is now being accused by Wilson's camp of never intending to fight on Sunday. 

'This feels like a stitch up,' Wilson's manager and Tszyu's long-time ex-agent Glenn Jennings said. 

'If you are serious and you sign a contract at 133, there is an expectation that you will deliver.

'It is not only unacceptable, it is a blight on the sport. This is professional, there is nowhere to go for this bloke now.'

Wilson was devastated at missing his potentially life-changing opportunity.

'I put my heart and soul into this sport. I train very hard,' the 30-year-old Queenslander said.

'It's uncontrollable for me. I did everything correct on my end.'

Undefeated Olympian Paulo Aokuso will move to the main card, taking on Luis Tejeda from the Dominican Republic in a light-heavyweight bout.

Wilson's fight is the second co-main event to be cancelled this week after Fulton's fellow American Jermall Charlo was denied a visa to face rising Australian Koen Mazoudier.