Calzaghe, right, beat Jones with a non-stop barrage of punches
Joe Calzaghe put on one of his finest displays to dismantle Roy Jones Jr at Madison Square Garden in New York in the early hours of Sunday morning.
Calzaghe was floored in the first round by a Jones right hand but thereafter assumed full control of the fight.
The Welshman opened a big cut over Jones' left eye in round seven and the 39-year-old was clinging on in the end.
All three judges scored the bout 118-109 in Calzaghe's favour to extend his unbeaten record to 46 fights.
Four-weight world champion Jones, of Pensacola, Florida, falls to 52 wins and five defeats and may now choose to retire.
Knockdown was 'a shock' - Calzaghe
Calzaghe was cheered on by an estimated 7,000 British fans out of a crowd of 14,000, including Lennox Lewis and former foes Bernard Hopkins and Mikkel Kessler, both hoping to lure the Welshman into continuing his career.
The 36-year-old, who was floored by Hopkins in their fight in Las Vegas in April, suffered the same ignominy again, walking onto a flashing left hook before ducking into what appeared to be a forearm to the throat.
"Yes, I was hurt, he caught me with a good shot. But that's what being a champion is all about - when you're put down on the floor, you come back stronger," admitted Calzaghe after the fight.
"It's an honour getting in the ring with Roy Jones, the guy is a wicked fighter and caused me a lot of trouble. I didn't see the punch coming, it was a good shot. It's the fourth time I've been down and come back strongly."
Calzaghe backed Jones onto the ropes in round two, unleashing with quick combinations, although the American seemed to be soaking most of them up with his gloves.
Jones was having some success on the counter and landed with a flashing right just before the bell before turning to the crowd and sticking his tongue out.
Round three had the crowd on their feet for the full three minutes, with Calzaghe getting through Jones' high guard with a lacerating right-left combination before Jones hit back with a booming left.
Calzaghe smiled, before holding his hands exaggeratedly low, swivelling from the waist and evading a rash of Jones punches.
Round four was equally enthralling, with Calzaghe again throwing the most punches and Jones having the occasional success on the counter.
Jones just missed with a swingeing right hand on the bell, leading Calzaghe to feign rubbery legs, and it looked for all the world as though the Garden had another classic on its hands.
However, Jones' work-rate tailed off dramatically in rounds five and six - while Calzaghe’s punch output did not.
Jones tested Calzaghe’s chin with one booming right uppercut in the sixth, but for the most part he was happy to lean on the ropes and block Calzaghe's punches with his gloves.
Roy Jones Jr was cut badly in round seven
Round seven was a disastrous one for Jones, with Calzaghe opening up a big gash over his left eye courtesy of two lacerating lefts.
The injury seemed to drain Jones of any belief and by round eight, Jones, who many had predicted would not be able to live with his rival's work-rate, was blowing hard and looking unsteady on his feet.
The final four rounds were something of a procession, with the once elusive Jones lumbering forward mummy-like and providing an almost unmissable target.
And the American fans were heading for the exits long before the final bell tolled, with their once-great hero reduced to a bloody mess.
The stats revealed that Calzaghe threw 985 punches to Jones' 475, landing with 35% to Jones' 33%, and was just about the story of the fight.
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