The fans, many of whom sported red, white and green attire, roared when the Mexican boxing legends Marco Antonio Barrera and Julio César Chávez were shown on the big screen at the Mandalay Bay Events Center on Saturday night.

They cheered even louder when, in the final undercard bout, Francisco Vargas of Mexico recorded a stunning ninth-round technical knockout victory over Takashi Miura of Japan to win the World Boxing Council super featherweight championship in a match that Vargas seemed on his way to losing.

The partisan crowd felt certain: Their native son, Saúl Álvarez of Mexico, known as Canelo, was going to deliver an emphatic victory over Miguel Cotto, his rival from Puerto Rico, in their middleweight bout.

Sure enough, Álvarez delivered, winning a unanimous 12-round decision to secure the WBC middleweight title. Álvarez won by scores of 117-11, 119-109 and 118-110.

The rivalry between Puerto Rico and Mexico has produced some true classics in the boxing ring. Many experts trace the rivalry’s origin to the 1981 brawl in which Salvador Sanchez of Mexico knocked out Wilfredo Gomez of Puerto Rico.

Other memorable Puerto Rico-Mexico bouts include Chávez’s 1992 knockout of Hector Camacho, and Felix Trinidad’s brutal 12th-round stoppage of Fernando Vargas in 2000.

Perhaps the most anticipated clash between fighters representing these two nations took place in 1999, when Oscar De La Hoya met Trinidad. But that match failed to live up to the hype, with Trinidad earning a majority decision in a lackluster bout.

Many observers were hopeful that Cotto, 35, and Álvarez, 25, would land in the classics category, given that both are considered elite offensive fighters. Before the bout, however, both boxers said that they would not allow the boisterous fans and the pressure of the rivalry affect them.

“I understand the magnitude of this fight and what it means for the history of Puerto Rico versus Mexico,” Álvarez said.

But, he added, “I’m not worried about the pressure.”

Just the same, Álvarez (46-1-1, 32 knockouts) was bullish on the prospects of the match living up to the legacy of the other Puerto Rico-Mexico classics.

“I know this fight will go down as one of the most exciting and explosive nights in the famed rivalry and in the sport of boxing,” Álvarez said.

Álvarez has spoken repeatedly, and at length, about wanting to earn the victory for his native Mexico. Cotto, too, has expressed a desire to win for Puerto Rico. But his primary motivation was more personal than nationalistic.

“I have to win for me, for my kids, for my family, and then for Puerto Rico,” Cotto said.

The intensity of the Puerto Rico-Mexico rivalry did not result in any personal animus between the fighters, who were cordial with each other throughout the promotion. They even shook hands after the staged face-off, which took place after the weigh-in and is designed to generate hostility.

Cotto (40-5, 33 knockouts) reserved most of his scorn during the week for the World Boxing Council. He was stripped of that sanctioning organization’s championship on Tuesday, when, according to a spokeswoman from Roc Nation Sports, which promotes Cotto, the fighter refused to pay a $300,000 sanctioning fee that the WBC was seeking.

“I don’t need their belt,” Cotto said of his decision. “I have enough belts in my house. And with the money I saved, I can buy any belt I want.”

The WBC’s No. 1 contender, Gennady Golovkin (34-0, 31 knockouts), watched the fight from ringside, hoping for an eventual fight with the winner. Before the match, Golovkin said that he did not favor either and did not have an opinion on which he would fare better against.

“Miguel has a lot of experience,” Golovkin said. “Canelo is a young superstar. Both great champions.”

Tom Loeffler, the managing director of K2 Promotions, which promotes Golovkin, was more optimistic about the prospect of his fighter getting a chance to face Álvarez rather than Cotto.

“I think Canelo at some point will definitely fight Gennady,” Loeffler said. “I think they’re on a collision course. Whether it happens next fight, two fights down the road, a year down the road, I think that’s going to be a huge fight.”

A huge fight to unify the middleweight title that, were it to take place, would hopefully be as action-packed as the one on Saturday night.