The 22-year-old Mexican retained his WBC super welterweight title with a dominant performance over his American challenger.
Comfortable title defence for Saul Alvarez with five round win over Josesito Lopez
Saul Alvarez has retained his WBC super welterweight title in Las Vegas after dropping challenger Josesito Lopez three times before finally stopping him late in the fifth round.
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 round.
The 22-year-old Alvarez - nicknamed Canelo - made his fifth title defence against a gritty but overmatched American opponent to take his record to 41-0-1, 30 by knockout.
"I am very happy with what I showed today," Alvarez said after the bout.
"In boxing you are always learning and I still have a lot to learn. But I will be better next time."
Alvarez kept Lopez trapped on the ropes for much of the fight, scoring 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.
Lopez, of Riverside, California, was fighting for a title for the first time in his career. He was a heavy underdog heading into the fight and it showed as he had lost 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.
"Canelo is a good fighter. 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."
Alvarez's game plan was to cut off the ring against Lopez who appeared to lose energy at the end of each round when the majority of the knockdowns took place.
He hit Lopez with a low blow in the fourth round which delayed the fight for about a minute while the American recovered.
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.
Marcos Maidana also stopped Jesus Soto Karass early in the eighth round to win their welterweight bout.