Saul ‘Canelo’ Alvarez knocked Rocky Fielding down four times in an emphatic third-round stoppage win in New York.
Alvarez, 28, was heavy favourite and brutal left hands to the body dropped his rival in rounds one and two, all but ending hope of an unlikely upset.
A stinging right to the jaw again downed Fielding in round three, before another left connected with the body, prompting the bout to be waved off.
Alvarez now holds a minor version of the WBA world super-middleweight title.
Despite the status of the WBA’s ‘regular’ title compared to the ‘super’ title Britain’s Callum Smith holds in the same division, Alvarez can now boast being a world champion in three weight divisions.
He still holds the WBC and WBA titles at middleweight – a division lower – and his move up 8lb only ever looked like ending in victory as he broke Fielding’s heart early on with a savage display of body punching.
“Fortunately for me he came to attack,” said Alvarez. “That was the error he made and I did my thing in there.”
With the likes of Hollywood actor Bruce Willis, tennis legend John McEnroe and world heavyweight champion Anthony Joshua ringside at Madison Square Garden, Alvarez quickly showed his intent by walking Fielding down to whip a left to the body which crumpled the Liverpudlian.
Despite boasting about six inches in height advantage, Fielding at no point established range, allowing the onslaught to continue into round two when he again got back to his feet from an almost identical body shot.
He fought back with combinations of his own in pockets but the shots carried minimal power with the fight being played out at Alvarez’s range, ensuring he smothered and soaked up anything that came back his way.
After a right which swept across Fielding’s jaw to down him in three, the Briton was told “one more” from the official and it duly arrived, again a left to the body.
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Fielding’s corner complained in the changing room of Alvarez prior to the bout, accusing the challenger’s corner of ‘stacking’ his hand wraps.
But after walking out in front of a crowd packed with Mexican support, Alvarez showed he was a cut above, extending his record to 51 wins and two draws, with his solitary defeat coming against Floyd Mayweather in 2013.
This was the first bout of a £278m, 11-fight, five-year deal which has made Alvarez the sport’s highest-paid fighter and no-one in attendance could doubt his talent, as he cleverly closed space and made punch after punch land with ferocity.
He had spoken prior to fight of joining a handful of boxers from his homeland to reign in three weight-divisions, but is widely expected to drop back down to middleweight, with fans calling for a third contest against Gennady Golovkin.
Afterwards, Alvarez said he thought their rivalry “ended” with his win in September following a draw in 2017. But he vowed to give fans the fights they wanted and unification bouts to add further belts look a certainty.
IBF world middleweight champion Daniel Jacobs was ringside and said: “With me being a champion, it’s a possibility I’ll fight him next year. I want to fight the best and earn the fans’ respect.”