If this is truly to be the fight which finally announces Shakur Stevenson as the future of US boxing, he must ruthlessly end the feelgood story of an American hero to achieve it.

Jamel Herring’s transition from the military to underdog world champion is a movie script in waiting but the twist is that Stevenson, his challenger, is at least a former associate and at best a former friend who now denies that any relationship ever existed.

Stevenson will challenge for Herring’s WBO super-featherweight championship in Atlanta, live on Sky Sports Main Event and Arena from 3.30am in the early hours of Sunday, in an absorbing contest between different generations which has turned nasty.

Stevenson, aged 24 and 11 years younger than the champion, is unbeaten and already a world champion in the division below – just four months ago he won a fight having trained and prepared in the same gym, with the same trainer, as Herring.

Both men knew this inevitable fight would happen but they spent weeks side by side, shunted together by circumstance, sharing what must have been an awkward closeness.

Stevenson has now vigorously and spitefully denied they were ever friends.

The common bond is the US Olympic team (Herring went to London 2012, Stevenson won silver at Rio 2016) and now the camp run by Brian ‘Bo Mac’ McIntyre where pound-for-pound great Terence Crawford rules as top dog.

McIntyre is Herring’s trainer, Crawford is Stevenson’s mentor.

It means McIntyre trained Stevenson for his previous fight, but is now plotting his downfall from Herring’s corner.

“It’s business,” he said.

Crawford has shrugged at this tricky scenario: “They are both my brothers.”

Stevenson has mocked Herring’s respectful reputation and sees it as a sign of weakness, saying: “I’m not one of those fighters that will say: ‘Hey Jamel’. It’s a fight.

“I promise you will not see me in the ring saying: ‘Hey, what’s up!’ We are not having a friendly fight.

“He likes fights where he can be friends with people.

“It’s not sparring, bro.”

Herring has refused to be baited by his young challenger, just condemning: “I’m upset at the character he is portraying.”

There has always been a glimmer of a young Floyd Mayweather in Stevenson’s brashness and in-ring skills. If that generous comparison holds any weight, tonight is the time to prove it.

Stevenson, who was scouted by Mayweather personally at the Olympics five years ago, has something special about him but hasn’t yet had the correct fights to bring it out of him. He has been criticised for performing within his capabilities but Herring’s experience and the personal edge to tonight’s fight could allow for a breakthrough performance.

He is about to welcome his first child with his partner, the rapper Young Lyric, and has warned Herring: “He’s trying to take food off my plate and I’m trying to take food off his plate. May the best man win. This is a fight.”

Herring is one of boxing’s most admirable souls. He is living proof that nice guys don’t always finish last, though he had to claw and scrape to eventually prove that.

“I carry myself with dignity,” he said in response to Stevenson’s trash talk. “Once a Marine, always a Marine.”

Herring, a New Yorker, joined the military due to 9/11 and served two tours of Iraq. The PTSD haunted him but boxing gave him “a gateway away from hell”. He steps in the ring every time thinking “about individuals who didn’t come home from those tours”.

He lost his two-month-old daughter in 2009 then, remarkably on what would have been her 10th birthday, he became a world champion against the odds by beating Masayuki Ito.

Herring had already lost two fights and never previously challenged for the top honours. He was not a fighter expected to reach such heights and he remains a proud overachiever, striving in memory of those who aren’t here to witness him.

“A lot of things drive me to who I am today,” he said. “A lot of people whose spirits I keep alive.”

The standout result of Herring’s career came earlier this year, at the age of 34, when he knocked down, stopped and eventually retired Carl Frampton. He denied Frampton a piece of Irish history on that night. He is someone who performs best when expected to lose.

But in Stevenson tonight, Herring will come up against an opponent whose ceiling is still unknown. There is real suggestion that Stevenson can become the face of American boxing for years to come but Herring is well-versed in upsets and this would be his greatest yet.

Sky Sports Boxing schedule

October 24 – Top Rank in Atlanta
Jamel Herring vs Shakur Stevenson – WBO super-featherweight title

October 31 – Top Rank in New York
Jose Zepeda vs Josue Vargas

November 6 – Top Rank in Las Vegas
Mikaela Mayer vs Maiva Hamadouche – IBF and WBO super-featherweight titles

November 6 – BOXXER in Liverpool
Super-lightweight tournament

November 20 – BOXXER in London
Richard Riakporhe vs Olanrewaju Durodola
Caroline Dubois professional debut

November 20 – Top Rank in Las Vegas
Terence Crawford vs Shawn Porter – WBO welterweight title

December 11 – BOXXER
Savannah Marshall
Claressa Shields vs Ema Kozin

December 11 – Top Rank in Las Vegas
Vasiliy Lomachenko vs Richard Commey

December 17 – Top Rank in Montreal
Artur Beterbiev vs Marcus Browne – IBF and WBC light-heavyweight titles

February 26 – Top Rank in Glasgow
Josh Taylor vs Jack Catterall – undisputed super-lightweight title