Saul "Canelo" Alvarez (left) knocks out Rocky Fielding for the WBA super-middleweight championship at Madison Square Garden in New York City on Saturday. Photo: IC

Mexican superstar Saul "Canelo" Alvarez brutally overpowered England's Rocky Fielding with a dominant display on his New York City debut on Saturday to become a three-weight world champion.

Alvarez, who is the reigning WBC and WBA middleweight world champion following his thrilling victory over Gennady Golovkin in September, had little trouble in moving up in weight class and defeating Fielding, who held a second tier version of the WBA's super-middleweight title.

Alvarez sent Fielding to the canvas in the very first round with a crunching body shot and remained in complete control. He delivered a similar punch in the second, which was also too much for the Englishman to take before the fight was stopped toward the end of the third following two further knockdowns.

"I thought he would use his distance but luckily he didn't," Alvarez said in the ring after becoming the ninth Mexican fighter to be a champion in three different weight divisions.

"He came to attack and I did my thing. The plan was to hit the body. That was the result," he said.

It was, ultimately, a total mismatch. Fielding just didn't have the power to compete, and when he went down twice in the third, referee Ricky Gonzalez correctly stopped the fight with 22 seconds left in the round.

It was a brave effort from the 31-year-old from Liverpool, who deserves great credit for accepting the task of entering the ring against the brilliant flame-haired Mexican, who extended his record to 51-1-2 with 35 knockouts in his first appearance since signing a record-breaking 11-fight, $365 million contract with sports streaming service DAZN.

This was Alvarez's first bout at super-middleweight. He fought Julio Chavez junior at a 164-pound (74 kilograms) catch-weight in a non-title matchup in 2017, and although he is set to move back down to 160 pounds for his next fight in 2019, his performance in front of a sold-out Madison Square Garden crowd was evidence of his ability to perform whatever the weight class.

Fielding, coming into the bout with just one defeat from 28, had won his previous six fights, including a memorable victory over Germany's Tyron Zeuge in July which brought him world title glory.

Yet the proud and rangy Liverpudlian, who possessed a five-inch (12.7-centimeter) height and reach advantage, was unable to cope with his opponent's supreme speed and punch power.

Fighting in the famed New York City arena for the first time in front of a vocal pro-Mexican crowd, Alvarez didn't disappoint.

The 28-year-old wasted no time in making his mark and when Fielding fell to his knees following a left to the body in the first there only looked like being one winner.

Fielding enjoyed some success but wasn't using his height to his advantage. Alvarez soaked everything up before sending his opponent down once more in the second with another crunching blow to the ribs. Towards the end of the third, Fielding was back on his knees and when he returned there once again soon after, there was no way back as crowd of 20,112 roared its approval.

The Mexican, competing in his second fight since completing a six-month ban for testing positive for a banned substance in March, has vowed to drop back down to middleweight next year, which could see a potential third fight with Golovkin become an exciting reality.