Triumphant Tszyu's credentials already being questioned

American Jermell Charlo has wasted no time questioning Tim Tszyu's credentials and pledged to "shut him up" when the two finally meet in an undisputed world title fight in Las Vegas.

Charlo was only mildly impressed with Tszyu's ninth-round TKO of his US countryman Tony Harrison in Sydney on Sunday night.

The victory earned Tszyu the interim WBO super-welterweight belt, which even the hometown hero seemed less than content with after the dust had settled on his savage victory.

"This is an interim belt. The champ has to be beaten and he's got all four belts," Tszyu said after extending his unbeaten record to 22 from 22 professional fights, with 16 knockouts.

"It's just a little step up on my journey, but the real undisputed for me is beating Charlo.

"This is just another step to where I want to be."

Where Tszyu wants to be is where Charlo is - owning his division.

"This boxing journey is incredible," he said.

"I went to America for 10 weeks, I'm only 28 years old - young. I'm enjoying myself. It's not the destination, it's the journey and the process.

"I'm loving every minute of it. I grind hard, I train hard. I do everything correctly."

But Charlo, who was supposed to fight Tszyu in January for all four straps before breaking two bones in his left hand, maintains the Australian challenger is not in his league.

Charlo said while "it was a good performance by Tszyu", he felt the 28-year-old merely "did what he had to do".

"He doesn't really show a lot of athleticism to me," Charlo said after commentating on the fight in the US for Showtime.

"When you have skills and you have style and you have power, that's when you get four belts.

"You see what I'm saying?"

Charlo, whose only defeat of his career so far came against Harrison in December, 2018, did concede it would be tough against Tszyu "because he's coming forward".

"But I think he's perfect for my style," he said.

"He fits suitably well for me. I know he can't take my punch because I know my punch is different.

"I think he's going to do the same thing (as he did against Harrison). He's not going to change up much.

"Seeing him tonight just made me want to fight and be back in there, to get this over with, to just shut him up.

"I've shut up a lot of fighters. He's just another one.

"I'm a different animal in there. You can't compare me to Tony.

"Tim is next."

Charlo's criticism is water off a duck's back to Tszyu, who has a new believer in Harrison.

"He's up for the challenge," Harrison said after facing a different fighter than the one he saw in Tszyu's previous tussle with Terrell Gausha last March.

"They've done a good job over there. His timing, his reaction is very good.

"He's still basic. He's definitely a lot sharper. He's sharp."

Harrison even offered to help if Team Tszyu came calling.

"Any way I can be of service," he said.

"Anyone who can help me in my situation now, whatever pays the bills for that route, is all I care about."