Tim Tszyu went from planning to fight Keith Thurman less than two weeks ago to getting ready for Sebastian Fundora as his opponent Saturday in Las Vegas, after Thurman suffered a biceps injury and Fundora was tabbed as his late replacement.

Tszyu, the WBO junior middleweight titleholder, was forced to switch his preparations for one opponent to those for a vastly different one. Thurman is an aging orthodox fighter who would have been making his 154-pound debut after having fought just once in five years. Fundora – a tricky 6-foot-5½ southpaw who is 10 inches taller than Tszyu and also sports a 10-inch reach advantage – is practically a different animal altogether.

The drama will unfold Saturday at T-Mobile Arena in Las Vegas. The junior middleweight fight (which will now also be contested for a vacant WBC 154-pound title) will headline a PBC show on Amazon Prime Video pay-per-view.

Oddsmakers like Fundora’s chances better than they did Thurman’s, even though Fundora was brutally knocked out in his last fight against Brian Mendoza – the same fighter Tszyu beat in his previous outing. Before the Thurman bout was scrapped, Tszyu was a -900 favorite to beat the +550 betting underdog Thurman, per DraftKings. Now, DraftKings lists Tszyu as a -525 favorite and Fundora as a +370 underdog.

“It's been a little bit of a shift,” Tszyu told BoxingScene. “Nothing has rattled me. It's brought out an inner beast in me that I am waiting to unleash.”

Still, Tszyu (24-0, 17 KOs) is aware of the contrasts, as well as the rare gifts Fundora (20-1-1, 13 KOs), nicknamed “The Towering Inferno,” brings into the ring.

“When you see a guy that tall, people say, 'How do you win against a guy like that?'” Tszyu said. “He's got such an advantage over everyone in the division. It's quite simple. So that all makes sense. When we get in there, it's completely different.

“He has long arms and is awkward. He's able to hit you from a lot of directions. His uppercuts. His constant punching – all of that will be a task.”

To quickly prepare for Fundora, Tszyu arranged a trio of sparring sessions against southpaws, one of which was 6-foot-4 contender Mykal Fox.

“It's just a little bit of a brain reshuffle with technique and gameplan,” Tszyu said. “If you want to be a champion and reach greatness, this is what you have to do.”

Tszyu, 29, also stated that there is no added pressure promoting his first stateside pay-per-view, because he has starred in 12 PPV events in Australia. 

A second-generation star, Tszyu will also have the support of his father, Hall of Famer Kostya Tszyu, who will be ringside Saturday night.

"I'm used to this. It's nothing out of the ordinary,” Tszyu said. “I want to stay consistent in my career. ... My next few years will be in America conquering this land.”

Just don’t expect Thurman to find his way back into the fold. As for the viability of “One Time” as a future opponent, Tszyu said that ship has sailed.

“Thurman is in the past and he's long gone for me now,” Tszyu said. “We've moved on. Simple. It's done.”

Tszyu also delivered a promise on how he plans to beat Fundora:

“Adapt, conquer and find the finishing shot,” he said. “Just don't blink."