Las Vegas, Nevada — Saul "Canelo" Alvarez stopped Josesito Lopez late in the fifth round Saturday night, defending his WBC 154-pound title with a relentless display of power from the 22-year-old Mexican star.

Alvarez (41-0-1, 30 KOs) ended Lopez’s dreams of a second upset victory this year by knocking down his 12-to-1 underdog opponent in the second, third and fourth rounds. Another series of relentless combinations finally forced referee Joe Cortez to step in with 5 seconds left in the fifth, sending Alvarez to his 37th consecutive victory.

Lopez (30-5) earned this unlikely title shot by knocking off Victor Ortiz in June, but the Riverside, Calif., native was simply outclassed by one of boxing’s most dynamic young champions. "Josesito has a big heart and is very brave, but I came in and did what I had to do and finished business," Alvarez said. "I’m not usually looking for the knockout, but tonight it was perfect."

Alvarez dropped Lopez with body shots in the second and third rounds while also absorbing everything Lopez could throw at him with barely a flinch. Alvarez knocked down Lopez with another combination with 15 seconds left in the fourth.

Cortez, a veteran official refereeing his final fight before retirement, stepped in when Lopez offered little resistance to a long barrage of shots. Alvarez paraded around the ring briefly on his cornermen’s shoulders while the pro-Mexican crowd roared one last time.

Even with an big crowd attending Sergio Martinez’s middleweight fight with Julio Cesar Chavez Jr. a few blocks down Tropicana Avenue at the Thomas and Mack Center, a sellout crowd of 14,275 packed into the MGM Grand Garden to watch Alvarez, whose redheaded good looks and furious punching power have put him in competition with Chavez for the top spot among Mexico’s most beloved fighters.

"I think I’m improving with each fight," Alvarez said. "I had a big responsibility tonight to all my fans watching around the world, and I think I did my job. I want the big fights now. (Miguel) Cotto, (Floyd) Mayweather, I’ll fight them all."

Alvarez was guaranteed a $2 million purse to just $212,500 for Lopez, although he’s likely to make more. Canelo even got the $100,000 bonus from promoter Golden Boy for the Knockout of the Night on a show dubbed "Knockout Kings," beating out Marcos Maidana’s sensational eighth-round stoppage of Jesus Soto Karass on a strong undercard.

Lopez earned this shot with a stunning upset victory in June over Ortiz, the former welterweight champion expected to be Canelo’s next opponent. Instead, Lopez broke Ortiz’s jaw in the win and eventually accepted the golden ticket to fight Canelo when Ortiz, Paul Williams and James Kirkland all couldn’t or wouldn’t take on the rising Mexican star.

"He proved that he’s the better fighter," Lopez said. "I felt good going in, but his size is pretty good. There was a big difference. He’s a smart fighter. I was hoping to land some punches, but he was smarter, stronger and patient. He was looking for a good punch to change the momentum."

Although Lopez had never fought at 154 pounds and was a junior welterweight last year, Alvarez insisted he wouldn’t overlook any opponent. Lopez spent most of his career fighting in hotel ballrooms and casinos in his native Southern California before stepping in against Ortiz under Staples Center’s bright lights when Andre Berto failed a doping test.

Lopez is slightly taller, but Alvarez’s rock-solid build presented a sharp contrast with Lopez’s more wiry frame — and Canelo made sure Lopez felt his power throughout the fight.

Alvarez won every round on every judge’s scorecard before the fight was stopped. The Associated Press also had Canelo winning 40-33.

Alvarez landed 52 percent of his 269 total punches, including 64 percent of his 162 power shots. Lopez actually threw more punches, but landed just 32 percent of his 279.

Lopez unloaded a series of shots early in the second round that backed up Alvarez, but didn’t appear to hurt him in the slightest. Alvarez replied with his typically heavy hands, putting Lopez on his back heel and eventually flooring him late in the round with a right to the face and a devastating left hook to the ribs.

Lopez went down again in the third, stumbling backward after a straight blow to the stomach. A combination basically forced Lopez to the ground in the fourth — and though he didn’t appear beaten, he also had little to offer.

"He’s a way better fighter than Victor," Lopez said of Alvarez. "He’s got a lot of skill, and he’s very smart."