Spence became and defended unified titles at welterweight, before Tszyu was crowned WBO junior middleweight champion.

Now, with their best days likely behind them, the two will lock horns on Sunday (Saturday night in U.S.) live on Amazon Prime Video and DAZN PPV from Sydney's Qudos Bank Arena in Australia.

Former two-time welterweight titlist Shawn Porter is intrigued by their middleweight contest. "It's perfect timing for both these guys," Porter told The Ring. "If Errol had beat Terence [Crawford], we would never see a fight between Tim Tszyu and Errol Spence. Tim tells me he's been looking to fight Errol for about five years ... I don't think this is a fight Errol ever expected to have, until what happened to him.

"I think it's a great fight but not necessarily a 50-50, more 60-40 and might be a little surprising to say, in Errol's favor. I think he's the better boxer and you cannot deny his pedigree. It's pretty clear his punch resistance is low for a number of reasons, but he's got more skill, experience and I think he's going to win.

Spence will end a three-year long layoff, having lost his unbeaten record and unified titles after a brutal ninth-round stoppage loss at the hands of Crawford in July 2023.

As well as that defeat, a well-documented high speed car accident four years earlier which saw him thrown from his Ferrari added to wear-and-tear on his body.

Porter feels the time off will have helped heal Spence mentally and physically, while Tszyu's form has been patchy.

"Even with how Errol looked in his last fight, it's been three years and there's so much you could say about that [defeat], while we've seen the best and worst of Tszyu. Most recently, we've seen the worst."

Porter spent time with former foe Spence, who beat him via split decision after a thrilling 12-round contest in September 2019, getting the opportunity to peek behind the mask at a former champion who immersed himself with other sporting activities — football and basketball — as well as family time to give himself peace of mind.

"A lot of times you can look at a fighter and know if they're not being straight with you, but I spent two or three hours with him. He says the lifestyle he had being out late and drinking is gone. I trust and believe if he has been living the lifestyle he says for the last three years, that rest is great.

"Sometimes the rest can be too much, but his body and mind have had enough time to heal. I know there were some things going on with him emotionally and personally that have passed by, on the other side of that he's a better person than when facing Terence and probably some of the fights prior."

Much like Tszyu outlined earlier this month, Porter concedes the 36-year-old would have been better served to have a warm-up bout before this outing. Nonetheless, he's confident his compatriot will rise to the occasion.

"I'm not surprised at all that Errol is coming back and immediately fighting a guy who has been active, yes [Tszyu has] been on the downside, but still active," Porter continued.

"He came back even after that [second] fight with Sebastian Fundora and has won twice. I'm not surprised Errol didn't have a comeback fight, but think he should have. He's leaning in on all the experience he has, and I understand that completely, but think he really needed to feel fight night to know he's ready for a big fight.

"I've retired, come back to the ring and coaches have asked me to spar for just a couple of rounds but it's much more than I expected. Even though he's relying on experience and training to get ready, he should have had one.

"One thing I know about Errol, he's a showtime fighter. When the lights come on and that bell rings, he's ready ... sparring is one thing but if there was someone who I would bet on to do it, I'd definitely put my money on Spence being out of the ring for three years, coming back and looking like he never left."