By Michael Bennett

Canelo Álvarez pummeled Julio César Chávez Jr., winning a unanimous decision last night in a Las Vegas fight that left no doubt about who is the leading active boxer from Mexico.

Álvarez (49-1-1, 34 knockouts) used a punishing jab to take control early in the bout, a 12-round matchup of former middleweight champions. Chávez (50-3-1, 32 knockouts) started bleeding from the nose in the third round. His left eye swelled in the sixth and started to close a round later.

Álvarez, a 4-to-1 favorite, was much quicker than Chávez, the largest fighter he has faced, and he won every round on all three judges’ cards.

Afterward, Álvarez, 26, immediately announced that he would face the middleweight champion Gennady Golovkin in September in a long-awaited bout. Golovkin then joined Álvarez in the ring.

Chávez, the 31-year-old son of the legendary boxer Julio César Chávez Sr., was trying to revitalize a career derailed by failed drug tests, weight issues and lax training. But he proved no match for Álvarez in the bout, which was fought at a catchweight of 164 ½ pounds.

Despite his four-inch height advantage and an obvious weight edge after he had rehydrated, Chávez was overmatched in his first fight under the renowned trainer Ignacio Beristain, known as Nacho.

A majority of the announced 20,510 fans inside the building wore either red (for Álvarez) or green (Chávez) headbands as they celebrated the fight and the Cinco de Mayo weekend by chanting “México, México.”