LAS VEGAS • The first punch Conor McGregor landed bloodied Donald Cerrone's nose.

It was a sharp right jab from the former two-division Ultimate Fighting Championship champion, in his first bout since October 2018, that sneaked between Cerrone's gloves.

Seconds later came the left-footed kick to the jaw that sent the fearless veteran reeling.

And then the punches rained down from McGregor as Cerrone sagged to the canvas, the bleeding speeding up.

The throttling did not stop until the referee, Herb Dean, stepped in to save the American, halting the main event of UFC 246 after just 40 seconds on Saturday night.

So, if you were wondering whether 15 months on the sidelines robbed McGregor of his signature punching power and panache, they were all still intact.

The 31-year-old had spoken of an emphatic win in the build-up, and "Mystic Mac" delivered.

The Irishman also pointed out afterwards that his win made him the first UFC fighter with knockout victories in three weight classes.

"I made history here tonight. I'm very proud of my accomplishment," McGregor said. "Etch my name in the history books one more time. For the Irish people. For my mum back home.

"I feel really good, but I came out of here unscathed. I'm in shape. We've got work to do to get back to where I was. I am very happy and very proud. Thank you all for your support."

McGregor, who took his win-loss record to 22-4, was the first UFC fighter to hold two championship - lightweight and featherweight - belts at the same time in 2016.

But he had not won since then - with only two bouts, a technical knockout boxing loss to American Floyd Mayweather and a submission defeat by Russia's Khabib Nurmagomedov - coming in between brushes with the law and announcements of retirements.

His lack of ring activity has, however, not diminished his star power, as evident by the raucous and heavily partisan T-Mobile Arena crowd.

It also stunned Cerrone, who entered the octagon with a height advantage of 8cm. He also had more experience fighting as a welterweight, with 10 bouts under his belt at that weight class, compared to just two for his opponent.

But when the fight started, McGregor, as he predicted, overwhelmed Cerrone with speed and precision.

"This happened this fast," the 36-year-old said. "He got me with an elbow straight away and then he head kicked me.

"I have never seen anything like the shoulder shot he hit me with. I was disorientated. Then he stepped back, I was bleeding and he head-kicked me. But I love this sport and I am not stopping yet."

McGregor has now set up several intriguing options for his next bout, including Jorge Masvidal and Justin Gaethje. There is also the potential for a blockbuster rematch later this year with the undefeated Khabib and UFC president Dana White believes "that is the fight to make".

Likening their rivalry to some of boxing's greatest contests, like Marvin Hagler v Thomas Hearns and Muhammad Ali v George Foreman, he said: "There's always somebody fun that we can match up with Conor and everybody wants to fight Conor.

"When you look at what makes sense, Conor was saying that going into the Khabib fight, he had a lot of personal stuff, some stuff self-inflicted, he had injuries, all these things going on.

"He's been obsessed with getting that rematch because he knows he wasn't 100 per cent right. This is a massive fight with global appeal."

Khabib is scheduled to defend his lightweight title against American Tony Ferguson at UFC 249 on April 18, so any rematch is unlikely to take place before the second half of the year.

In the meantime, Mayweather would also like a piece of McGregor again, teasing the possibility of another fight on his Instagram page.

NYTIMES