LAS VEGAS >> Josesito Lopez threw every punch he could muster at Saul Alvarez, and Canelo barely flinched. A few moments later, Lopez was seated on the canvas with a sore midsection and a growing sense of doom.

The 12-to-1 underdog just wasn’t going to conjure up his second upset of the year. Lopez’s Rocky story would have no sequel.

Alvarez stopped Lopez late in the fifth round Saturday night, defending his WBC 154-pound title with a relentless display of power from a 22-year-old Mexican star who’s ready to fight boxing’s biggest names after dominating one of its most unlikely contenders.

Alvarez (41-0-1, 30 KOs) methodically erased Lopez’s improbable title hopes by knocking down Lopez 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.

“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.”

Lopez (30-5) earned this unlikely title shot by knocking off Victor Ortiz in June, but the Riverside, Calif., native realized he was simply outclassed by a dynamic young champion.

“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. I was looking for a good punch to change the momentum.”

Lopez got into the MGM Grand Garden by breaking Ortiz’s jaw and eventually accepting 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.

His life story — rising from boxing anonymity and keeping his family together while his father serves a major stretch in prison — is an inspiration, but Lopez realized pretty quickly he wasn’t about to add another unbelievable chapter.

Alvarez wouldn’t allow it. He has his own dreams of superstardom, and he’s well on the way.

“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.”

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.

Alvarez dropped Lopez with left hooks to the body in the second and third rounds while also blankly absorbing everything Lopez could throw at him. 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.