Conor McGregor reacts after winning his fight against Donald Cerrone. -Reuters

LOS ANGELES: Conor McGregor made a triumphant return to the UFC octagon on Saturday, pummelling Donald "Cowboy" Cerrone for a technical knockout victory in just 40 seconds.

The mixed martial arts superstar from Ireland — returning to the Ultimate Fighting Championship for the first time since he was battered into submission by arch-rival Khabib Nurmagomedov in October 2018 — overpowered his American foe without ever being tested.

After missing with a first punch, McGregor immediately bloodied a clinching Cerrone's nose with an upward shoulder strike — quickly followed by another.

Conor McGregor lands a knee to the face of Donald Cerrone in the first round in a welterweight bout during UFC246 at T-Mobile Arena in Las Vegas, Nevada. -AFP

As soon as Cerrone stepped back, McGregor caught him on the jaw with a high kick, then buried him under a hail of punches.

Referee Herb Dean stepped in to call a halt to the welterweight bout 40 seconds into the first round at the T-Mobile Arena in Las Vegas.

McGregor took his record to 22-4 with his first UFC victory since 2016, when he stopped Eddie Alvarez in a lightweight title fight to become the first fighter in UFC history to hold two championship belts at the same time.

That triumph was followed by a loss to boxing great Floyd Mayweather in a cross-combat superfight in 2017, his loss to Nurmagomedov, announcements of retirements and returns to fighting and brushes with authorities outside the octagon.

Conor McGregor celebrates his first round TKO victory against Donald Cerrone in a welterweight bout during UFC246 at T-Mobile Arena in Las Vegas, Nevada. - AFP

He pleaded guilty to hitting a man in a bar in Ireland and was accused of smashing a fan's phone in Florida.

The New York Times reported he is the subject of two alleged sexual assault investigations in Ireland.

Nevertheless, he remains the most popular fighter in UFC history, and his return brought out stars including British heavyweight Tyson Fury and New England Patriots superstar quarterback Tom Brady for the sold-out show.

In Cerrone McGregor faced an experienced veteran whose 36 wins included the most knockouts (20) in UFC.

Although there was no title at stake, McGregor said the outcome was a harbinger of things to come.

Conor McGregor hugs Donald Cerrone after his first round TKO victory in their welterweight bout during UFC246 at T-Mobile Arena in Las Vegas, Nevada. -AFP

"I like this (welterweight) division," he said. "I feel really good. I came out of here unscathed. I've got work to do to get back to where I was."

And while the UFC has stripped him of titles before, McGregor noted they can never take away the fact that he has posted knockouts in three divisions -- featherweight, lightweight and welterweight.

"Etch my name in the history books one more time," he said.