Thomas Hearns and Marvin Hagler, two warriors who once engaged in the most ferociously violent first round of boxing, were reunited a few years ago at the Kronk Gym in Kentish Town, north London.

The atmosphere was rich in nostalgia and bonhomie. “What you been doing, Marvin?” Hearns asked. Hagler responded that he was making movies in Italy, playing a Rambo-like character. “It’s not all about the money, Tommy,” he insisted. “It gives me something to do.”

Then Hagler asked Hearns what he was doing. “I still want to fight,” replied the 42-year-old Hitman. Hagler was shocked. “Man, you are crazy,” he said. “You ought to think about doing something else. You need to move on with your life.”

Hearns ignored the advice and competed in two more bouts, the most recent only two years ago. He was 47, a sad remnant of a bygone age that the respected American sportswriter George Kimball has revisited in his excellent book Four Kings: Leonard, Hagler, Hearns, Duran And The Last Great Era Of Boxing. “They didn’t set out to save boxing from itself in the post-Ali era, but they did,” Kimball wrote. “The conclusion of the rivalry among the Four Kings precipitated an almost immediate decline in the sport.”

There were nine bouts in various combinations contested by Sugar Ray Leonard, Hagler, Hearns and Roberto Duran, but the opening round of “The Fight” between Hagler and Hearns, Kimball noted, “remains the standard against which all others are measured”.

Hugh McIlvanney described that first round as “probably the fiercest, most devouringly competitive ever seen in a major professional fight” and Leonard would reflect that “if I ever needed a reason to stay retired, this was it”. Harry Mullan, then editor of Boxing News, told McIlvanney: “I was praying for it to end; I thought I was going to have a heart attack.”

For three minutes, which seemed to last forever, the world middleweight champion walked through Hearns’s best punches and consumed the ring with an unremitting rage, pinning his challenger on the ropes and unleashing a flood of punishment. Hagler suffered a deep cut in the middle of his forehead and blood was streaming down his face when the bell intervened.

There was more damage done to Hearns than weakening his spirit. Emanuel Steward, Hearns’s trainer, told Kimball: “When Tommy came back to the corner after the first round, he told me, ‘My hand’s broke’, but the idea of quitting never entered my mind. That just wasn’t who Thomas Hearns was. Tommy didn’t even go to hospital that night because word would have leaked out and he said he didn’t want to take anything away from Hagler’s performance.”

Only recently was that broken right hand revealed by Steward; Hearns had never spoken publicly of the injury. Over the next two rounds he was broken down by Hagler’s remorseless attack, though only after Marvelous Marvin had survived his own crisis in the third. Blood was pouring from the wound on his forehead when referee Richard Steele told the timekeeper to stop the clock so that ringside physician, Donald Romeo, could assess if he was fit to continue. Kimball wrote: “The champion would later claim that he told Romeo, ‘I ain’t missing him, am I?’ But tapes of the doctor’s visit to the corner suggest that, if Hagler did utter that now classic line, he must have been a better ventriloquist than he was a boxer.”

Within a minute of hostilities being resumed, Hearns was flat on his back, looking up at the night sky over the ring at Caesars Palace in Las Vegas, seeing stars. Having been stunned by a right hand to the jaw, he was chased to the ropes by Hagler, who floored him with two more concussive rights to the chin.

Hearns staggered to his feet at the count of nine, but Steele saw the blank expression in his eyes and stopped the fight at 1min 52sec of round three. “I’ve been refereeing for 15 years and I don’t think I’ve ever seen that much intensity in a fight,” he declared.

“All the money towards the end went to Hearns and actually made him the favourite,” reported Gene Mayday, the proprietor of Little Caesars sports book on the Strip, whose original line for a Hagler win by third-round KO was 25-1. “Hagler’s people started betting it at $1,000 or more a pop, so it went down. But, hell, they kept betting it. We got killed.”

Hagler had claimed the world middleweight title from Alan Minter in 1980 at Wembley. His 11th title defence was the most satisfying moment of his career. “Larry Merchant, the HBO TV boxing analyst, never gave me credit, and this really hurt me,” Hagler reflected. “He never told people about the great champion I was. He’d say I still hadn’t proved myself. So after the fight with Tommy, I asked him, ‘Do you think I’m a great fighter now?’ He replied, ‘Well, Marvin, I have to tell you that you are’.

“The way people in the business held back that recognition from me just made me meaner and meaner. How many fights does it take to become champion? That’s what I thought going into that fight.”

Two years later Hagler lost a disputed points decision against Leonard and never fought again. Hearns, who had held world titles at welterweight and light-middleweight before challenging Hagler, went on to win belts at middleweight, super-middleweight and light-heavyweight. But the biggest defeats of his career against Hagler and against Leonard in 1981 became his demons, which not even a draw against Leonard in their 1989 rematch could exorcise. He fought 17 more bouts, winning 15.

Hearns lives in Southfield, a wealthy suburb of Detroit, and has houses in Phoenix, Arizona, and Henderson, Nevada, just outside Las Vegas. He also owns a 46ft boat moored on the Detroit river, and, like Hagler, leads a happy life. Steward says: “You can see he’s very comfortably fixed. He has a big, beautiful house on about 10 acres and buys a new Bentley every year.

“I run into Marvin from time to time when I’m in Europe. He seems content. He drinks a bottle of red wine a day, but gets up at five in the morning to run and still looks in shape. The only dissatisfaction in his life, I’d say, is that he’s still bitter about the Leonard decision. He still believes he won that fight and they stole something from him. I doubt if he’ll ever get over that.”

Four Kings: Leonard, Hagler, Hearns, Duran And The Last Great Era Of Boxing, by George Kimball is published by Mainstream at £10.99.

ESPN Classic, Sky channel 442, will show Big Fights: Thomas Hearns at 8.15pm today

Explore More Sport

• Athletics

• Boxing

• Cycling

• Sailing

• US Sport