Conor McGregor has won his UFC comeback fight in Las Vegas with a first-round knock-out of Donald Cerrone.

The Dubliner defeated the American 'Cowboy' in a welterweight bout that ended after just 40 seconds due to a technical knock out. 

McGregor bloodied Cerrone's nose in the opening few seconds of the fight with a couple of unorthodox shoulder strikes.

He then stepped back and a head kick high over the guard landed square on the jaw of Cerrone, who fell to the floor and was left covering up as the Irishman rained down punches, prompting an early stoppage.

It was the 31-year-old's first fight since losing to Khabib Nurmagomedov in October 2018.

Fans waved Irish flags and chanted 'olé olé’ as he entered the arena.

Following his win, McGregor thanked his fans and said he was dedicating his win to the Irish people and his mother back home in Ireland. 

"I've etched my name in history one more time, for the Irish people and for my ma back home," he said.

"I made history here, I set another record: I'm the first fighter in UFC history to secure knockout victories at featherweight, at lightweight and now at welterweight, so I'm very, very proud of that.

"Donald holds the record for most head-kick knockouts, I'm so happy to get him down with a head kick myself. I'm very, very happy, very proud.

"Who's going up and down divisions and stopping people like that?

"The UFC can strip fighters and gift other fighters make-believe belts in order to replicate my champ-champ status, but they can't give knockout victories across multiple weight divisions. Etch my name in history one more time." 

Over the last two years McGregor has been making headlines for all the wrong reasons with court appearances on both sides of the Atlantic. 

In July 2018 he pleaded guilty to disorderly conduct after throwing a metal handcart at a bus carrying UFC fighters in New York. 

In November that year, in Dublin, he was disqualified from driving over a speeding offence.

Last March he was arrested in Florida after being accused of a smashing a man's phone.

And in November he was convicted of assaulting a man in a Dublin pub.

Asked about fans back home who have been disappointed by his behaviour outside of the octagon, he told RTÉ News that Irish people celebrate his successes and call him out if he lets them down. 

"That motivates me to keep working and be the man I want to be," he said. 

"I know some of the things have been not right, I owned up to that and we move on."

The president of the UFC Dana White said a future McGregor fight may take place outside of the US, possibly in the UK. 

McGregor responded by saying if one of his fights is happening in Europe, he wants it to be held in Ireland.