Khabib Nurmagomedov defeated Conor McGregor in the fourth round of their eagerly anticipated UFC lightweight title fight – before inciting a mass brawl by vaulting over the Octagon to attack his rival’s corner.

After McGregor tapped out due to a neck crank late in the fourth, Nurmagomedov stepped away from his prone rival and immediately pointed at the Irishman's corner, shouting and throwing his mouthpiece.

He then jumped over the Octagon and became involved in a physical altercation with Dillon Danis, a Bellator welterweight who trains with McGregor. The pair were eventually separated by police officers.

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Meanwhile, three members of Nurmagomedov’s entourage took advantage of the chaos to make their way into the Octagon and attack McGregor. UFC flyweight Zubaira Tukhugov was one of those involved, striking McGregor on the back of the head before he was dragged away.

UFC President Dana White later confirmed that three members of Nurmagomedov’s team had been arrested, although McGregor decided against pressing charges. White added that any UFC fighters involved in the attack would never fight for the promotion again.

The incident cast a dark shadow over the sport of mixed martial arts on an evening that had been billed as the biggest in the history of the UFC.

“I've been doing this for 18 years and I couldn't be more disappointed,” White commented at the post-fight press conference.

“I should be in here bragging about the pay-per-view but I haven't even looked at that or talked about it with anybody.

“We should all be celebrating how when you put on the right event with the right guys at the right time, it works.

“It was a very good week for everybody. It just sucks to end it like this, instead of celebrating we're saying 'that was pretty s***'.”

Security guards and police officers took several minutes to bring the situation under control, with both fighters given an entourage out of the T-Mobile Arena among ugly scenes in the stands.

McGregor was soundly beaten by his long-term rival (Getty)

Nurmagomedov also became involved in a heated altercation with White, who had refused to present him with his UFC lightweight title inside the Octagon because of security concerns.

At the post-fight press conference – which McGregor did not attend – Nurmagomedov apologised for instigating the brawl although laid the blame directly at his opponent’s door.

The 30-year-old, who extended his professional record to 27-0, said: “First of all I want to say sorry to Nevada Athletic Commission and second to Vegas. I know this is not my best side. I'm a human being.

“But I don't understand how people can talk about how I jump on the cage. He talked about my religion, he talked about my country, he talked about my father.

Khabib could yet be stripped of his title (Getty)

“He came to Brooklyn and he broke a bus, he almost killed a couple of people. What about this s***? Why do people talk about me jumping over the cage? I don't understand.

“This is a respectful sport, not a trash-talking sport. I want to change the game, you cannot talk about religion, about nationality.”

He took just one question before leaving.

The brawl overshadowed a dominant performance from Nurmagomedov, who defended the UFC lightweight title for the first time with an almost flawless performance.

Nurmagomedov took down McGregor in an attritional opening round, before staggering his rival with a huge overhand right early into the second.

McGregor did land a flying knee, only for Nurmagomedov to again take the fight to the ground, improving his position throughout and raining down blows on his prone opponent.

Both of McGregor's defeats have come by submission (Getty)

Nurmagomedov then decided to stand and strike with McGregor in the third, a round that the judges all scored in McGregor’s favour.

However that ultimately counted for nothing, with the Russian winning the fight via submission in the very next round. A takedown in the fourth signalled the beginning of the end, with a fatigued McGregor giving up his back and eventually losing via neck crank – the fourth submission loss of his celebrated career.

Who the two fighters challenge next remains to be seen given the plethora of legal problems thrown up by the chaotic post-fight brawl – although McGregor’s coach immediately shot down suggestions the Irishman could retire after this comprehensive defeat.