LAS VEGAS -- Canelo Alvarez entered the ring the best pound-for-pound boxer in the world and also the sport's biggest attraction. But now, for the first time in his career, he can call himself something else: undisputed champion.

Alvarez promised to punish Caleb Plant, and on Saturday he did just that with an 11th-round knockout victory at a sold-out MGM Grand Garden Arena to unify all four 168-pound titles.

A left hook followed by a brutal right uppercut sent both of Plant's gloves to the canvas in the penultimate round. He never recovered. On unsteady legs, Plant (21-1, 12 KOs) attempted to escape danger, but Alvarez sensed the moment. He closed in with a barrage of shots that dropped Plant a second time as referee Russell Mora halted the bout at 1:05 of Round 11.

"It means so much to me, for the history of Mexico, to be an undisputed champion," said Alvarez, who earned a guaranteed $40 million. "My respect to Caleb Plant. He's a very difficult fighter with a lot of ability. I do respect the fighter.

"We're men at the end. He wanted to continue. I said, 'There's no shame. We had a great fight today.'"

Plant, who earned a career-best $10 million, was transported to University Medical Center for observation, according to a PBC spokesperson. He was behind on all three scorecards at the time of the stoppage: 96-94, 98-92 and 97-93. ESPN scored it 98-92.

Alvarez (57-1-2, 39 KOs) broke Plant down with relentless pressure and a dedicated body attack, a strategy he has used time and again on his way to the top of the sport. The entire left side of Plant's body was red early in the fight as Alvarez continued to dish out blows to the midsection. Plant utilized a strong jab and deft footwork to keep Alvarez at bay and make him miss, but he rarely made Alvarez pay.

Plant, a 29-year-old native of Nashville, is regarded for his defensive ability, not his power, and it showed. The punches never gained Alvarez's respect, who swarmed, round after round, even as his elusive opponent glided around the ring.

The pressure mounted, and Alvarez didn't stop coming. It was simply a matter of time. The elusive fourth belt would soon be his.

"He was making things a little difficult, but [trainer] Eddy [Reynoso] told me, 'Let's keep with the game plan in the last two rounds here,'" Alvarez said. "And in the end, I got him. That's the way it had to finish. He was already hurt, and I went in for the kill."

He also got what he has long searched for: undisputed status. Alvarez won two super middleweight titles with a December victory over Callum Smith and picked up a third when he shattered Billy Joe Saunders' orbital bone in May. After that victory, it was clear whom he wanted next: "I'm coming, my friend," Alvarez warned Plant then.

And Alvarez never stopped coming once he lured Plant into the ring. The outcome was never in doubt, though Plant boxed well over the first few rounds. His use of feints, an educated jab and smooth footwork allowed him to stay off the ropes and, mostly, out of harm's way. But Alvarez is known for being a methodical starter, and Plant has a reputation for slowing down late in fights.

The matchup was originally being eyed for Sept. 18, but at the 11th hour, the deal fell apart. Alvarez then entered talks for a light heavyweight title challenge from Dmitry Bivol, but before a deal could be completed, Alvarez decided to delay his return until November so he could chase the fourth super middleweight title, which belonged to Plant.

When they finally faced off at a promotional event in September, chaos ensued. After Plant hurled insults at Alvarez, Alvarez responded with an open-handed left hand. Plant went after Alvarez, too, but emerged with a small cut under his right eye. Alvarez was left with deep personal disdain for Plant, who disrespected his beloved trainer, Eddy Reynoso, and called Alvarez a cheater.

The accusation was a reference to Alvarez's positive test for the banned substance clenbuterol that postponed his May 2018 rematch with Gennadiy Golovkin and led to a six-month suspension. Alvarez blamed the adverse finding on tainted meat consumed in his native Guadalajara.

Plant, ESPN's No. 3 boxer at 168 pounds, is the first champion in Al Haymon's PBC stable to earn a crack at Alvarez, but he might not be the last. The deal between Canelo and PBC is for one fight, but there's reason to believe Alvarez will continue to face off against Haymon's boxers. David Benavidez, ESPN's No. 2 super middleweight, is aligned with PBC, as is Jermall Charlo, the middleweight champion who plans to jump to the 168-pound division in the near future.

A third meeting with Golovkin, though, is the biggest fight of all. They clashed twice for the middleweight championship after Alvarez unified titles at 154 pounds. He also won a title at 175 pounds, where he could seek a bout with Artur Beterbiev.

It's less clear where Plant is headed after his first career loss. He won the title with an upset decision victory over Jose Uzcategui in January 2019 and defended it three times against light opposition. The fight with Alvarez was a quantum leap in competition. He fared well early, but in the end, Alvarez was too much.

It's a familiar story since Alvarez lost to Floyd Mayweather in 2013, and at this point, there doesn't appear to be anyone on the horizon who can dethrone him.