Poker fan Nathan Cleverly ready to go all in against Badou Jack on Floyd Mayweather-Conor McGregor undercard

Victory in his Las Vegas debut was only a few hours old but there was only one thing on a young Nathan Cleverly's mind as he stepped out to celebrate on the famous strip that night.

At 21 years old, the promising fighter from Cefn Fforest was handed a place on the undercard of Joe Calzaghe's clash with Bernard Hopkins at the Thomas and Mack Center on April 19, 2008.

It was the start of a love affair with Vegas for the kid from the Valleys who kept up his side of the bargain by beating North Carolina's Antonio Baker over eight rounds in front of a nearly empty stadium in the late afternoon.

But he was not in the mood for any of Sin City's more extreme pursuits that evening. Instead, the maths graduate broke away from the celebration party for a few crucial hours of solitude.

“I won my fight and I was on a high - high on life and embracing Vegas life,” he says from his hotel suite here at the New York New York, where he is occasionally interrupted by the rumble of the hotel's inbuilt rollercoaster thundering past the window.

“But I went off on my own afterwards. I remember just being on my own and loving it.

“I entered a few poker tournaments that night. I did OK. I didn't make the final table but I was enjoying the moment. I didn't care where I came. I was out on my own and loving it.”

This time the stakes for Cleverly are altogether higher as he defends his WBA light-heavyweight title against Badou Jack, the Floyd Mayweather promoted star, on the undercard of the 40-year-old's clash with Conor McGregor here on Saturday.

So it is appropriate that he uses a poker metaphor when he describes his perilous situation against Jack.

“I'm all in with this fight,” he adds. “If you win you're in the big time.

“There are a lot of world champions in boxing but to break through to that elite hierarchy, which is what the top fighters love, then I have to win this fight.

“I probably won't reach this level again if I lose. It's now or never for me.”

Back in 2008, Cleverly was part of Calzaghe's camp, which was located on the outskirts of Las Vegas, far from the fun and games of the strip.

This time is slightly different, with he and trainer Darren Wilson plotted up in the middle of the madness at New York New York, that rollercoaster not withstanding.

“I've been here since Thursday,” he says. “We were in the MGM first and then we moved over the road to New York New York, it's nice.

“We've been doing a few runs around here. Today we ran literally up the strip, dodging past people as we went. It's not ideal but it will do.

“In 2008 I was out here for just under two weeks and it was all focus before the fight. I stayed away from the vibrancy of the Strip. I stayed on the outskirts.

“Myself and Joe were sparring. I didn't really get a feel for the enjoyment side of Vegas until the day after the fight.

“I like the vibrancy of the place - it's got everything that I like. It's got the boxing side of it and the poker. It's the capital of boxing. If you want to be big in boxing you come to Vegas.”

And it just so happens that such a defining fight has landed on arguably the biggest spectacle combat sports has ever known.

But while Mayweather-McGregor could be described as the biggest mismatch in boxing's storied history, Cleverly-Jack is an archetypal 50:50 fight.

Former WBC super-middleweight champion Jack, who has already beaten George Groves and drawn with James DeGale in that division, is making his debut at the 175lb light-heavyweight limit.

Cleverly, a two-time world champion, had to wait until just two weeks ago for official confirmation of the clash after months of talks.

He said: “When you want a big fight you are going to have to stay patient at some point because it takes a long time to make them.

“I last fought in October, it's now August. It has been a long time but I stayed confident, mentally strong and focused.

“I was still training because I knew this fight was going to happen, it was meant to be. When he announced he was moving up to light heavyweight I thought it's the perfect opponent for us. He's a big name, he's established and I'm established.”

When asked to discuss the finer points of the challenge that Jack will pose, Cleverly shuts his eyes tightly as if recalling some of the many hours of tape in the bank.

“He does the basics very well, Badou Jack,” he says, eyes still closed.

“He's very solid in every department. Nothing special but very solid in every department, well-schooled, good technique and does the basics well. This is a very good opponent.

“But this is my eighth world title fight. Would I have the patience and character to do my little fights and get my way back up if I lose? I've already done that.

“It has been a great journey - nearly 10 years have flown by since I last fought here. I'm at the highest level and I'm here to stay. Defeat is not an option.”