Saul 'Canelo' Alvarez knocked Rocky Fielding down four times in an emphatic third-round stoppage win in New York.
Mexican Alvarez was heavy favourite and brutal left hands to the body dropped the Briton 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.
The 28-year-old 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 resolve 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 British 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 31-year-old 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 warned "one more" would bring an end to things by the official and it duly arrived, again a left to the body.
"I stood there too long, thought I could mix it with him and shouldn't have," Fielding said. " With my height, I should have kept the fight long, at distance. The better man won."
Unified heavyweight world champion Anthony Joshua: "Big respect to Fielding. What does he have to loss. A loss isn't a loss if you build from it and I'm sure he will build from it for sure."
British lightweight Tommy Coyle: "Canelo is a special fighter. I'm proud of Rocky tonight. Every time he got hurt and put down he got up and got braver. Well done mate. Not many can say they headlined at MSG."
British trainer Dave Coldwell: "Rocky went out on his shield. Can't ask more of a man than to try his best when fighting above his levels. Canelo is some fighter."
British super-middleweight Chris Eubank Jr: "Never seen someone look so happy to lose their world title."
Former two-weight world champion Carl Frampton: "He fought the absolute elite. The biggest star in boxing, and he was brave. Head high Rocky Fielding"