LAS VEGAS (AFP) — Terence Crawford stunned Mexican superstar Saul "Canelo" Alvarez to claim the undisputed super middleweight world boxing crown on Saturday, becoming the first man to win undisputed titles in three weight divisions.

In a fight of razor-thin margins, Crawford poured it on in the closing rounds to earn a unanimous decision victory, improving his unblemished record to 42-0 with 31 knockouts.

Crawford, 37, had jumped up two weight categories to vie for history, having already counted undisputed titles at super lightweight and welterweight among his titles in four — now five — weight classes.

He silenced critics who claimed his sparkling resume was packed with sub-standard opponents and quieted a raucously pro-Alvarez crowd of 70,482 at Allegiant Stadium, home of the NFL's Las Vegas Raiders.

Judge Steve Weisfeld scored the bout 116-112 for Crawford, while Tim Cheatham and Max DeLuca scored it 115-113 for the American, who had nothing but praise for his opponent.

"Canelo is a great champion," Crawford said. "I've got nothing but respect for Canelo. I'm a big fan of Canelo and he fought like a champion today."

Alvarez, 35 and a world champion in four divisions, fell to 63-3-2.

Crawford frustrated Alvarez with his agility and speed, losing none of his quickness as he stepped up to the 168-pound (76.2-kg) category.

He weighed in at the same 167.5 pounds as Alvarez, a career high for Crawford, who had never fought above 147 pounds until last year when he weighed 153.5 in a unanimous decision victory over Israil Madrimov.

Alvarez, boxing's biggest star for the past decade, simply couldn't get at him as Crawford used his jab and landed combinations with a vengeance in the closing rounds after wearing the champion down.

Crawford raised his arms and then sank to his knees when the final bell rang, having earned grudging admiration even from the pro-Alvarez crowd.

The Mexican, who will reportedly make $100 million for the fight, suffered his first defeat since dropping a unanimous decision to Dmitri Bivol in May 2022 in a bid at light heavyweight.

"A defeat does not define me," Alvarez insisted as he opened the door to a rematch.

"Crawford is a great fighter, and you have to give him credit. But I feel the same... I feel good sharing the ring with great fighters like him. If we do it again, it will be great."

There was little to separate the two through the first six rounds.

In a measured first round from both fighters Alvarez landed one solid body shot and he pressed forward more aggressively in the second round, continuing to work the body in a bid to slow the challenger down.

The action was picking up in the fourth, Crawford landing more combinations and proving a slippery target.

Crawford's hand speed was making difference in the sixth, and in the seventh he was making use of his longer reach and outworking the champion, who came off worse in most exchanges.

Both fighters came out firing in the ninth, Crawford punishing Alvarez with a string of combinations.

The American was shaken by an accidental headbutt, but he continued to pour it on and Alvarez could find no answer.

"Thank you," Crawford told the fans. "Thank you to all the supporters, thank you to all the haters. We made this a great event."

The bout was promoted by Saudi Arabia's Riyadh Season, which inked Alvarez to a four-fight deal that made him the latest in a growing list of boxers to flock to the kingdom for mega paydays.