Saul "Canelo" Alvarez kept his WBC super welterweight title on Saturday by knocking challenger Josesito Lopez down three times before stopping him late in the fifth round at the MGM Grand Hotel.

Mexico's Alvarez had Lopez bleeding from both the nose and mouth as referee Joe Cortez stopped the one-sided fight with five seconds remaining in the fifth.

The 22-year-old Alvarez, who is notable for his red hair, freckles and thunderous punching power, made his fifth title defence against a gritty but overmatched American opponent.

"I am very happy with what I showed today," Alvarez said.

"In boxing you are always learning and I still have a lot to learn. But I will be better next time."

Alvarez was the more aggressive fighter from the opening bell in the 154-pound (70kg) fight as he kept his perfect record intact, improving to 41-0-1 with 30 knockouts.

He continually trapped Lopez on the ropes where he battered the challenger with multiple punch combinations that led to the knockdowns.

He floored Lopez down with a left hook to the body in the second round, again in the third and fourth and then put the finishing touches on with a right to the head in the final round that forced referee Cortez to step in.

Californian Lopez was fighting for a title for the first time and his underdog status was confirmed in losing every round on the judges' scorecards.

Lopez, who moved up in weight to fight Alvarez, dropped to 30-5 in his career. He said fighting at 154 pounds was too much for him.

"He proved he is a better fighter," Lopez said.

"It is way out of my weight. I felt good, but the size was different for me."

On the undercard, IBF bantamweight champ Leo Santa Cruz retained his title by stopping two-time world champion Eric Morel in the fifth round.

Daniel Ponce De Leon also claimed the WBC featherweight belt by taking a unanimous decision from former champ Jhonny Gonzalez.