Lightweight champion Khabib Nurmagomedov made good on his promise in the main event of UFC 229 and wholly outclassed the Dubliner with a masterful performance, submitting McGregor with a rear-naked choke in the fourth round.

But having shown so much of his best, the Dagestani spoiled it all by launching himself into the crowd to attack McGregor’s support staff and kicking off a disgraceful brawl outside and inside the cage. The most shameful act of many came when members of Nurmagomedov’s camp jumped into the octagon to then attack a blind-sided McGregor.

The UFC had used the tagline ‘The world is watching’ for what was the richest night in its history. As security and police tried to restore some semblance of calm amid the disgrace, the organisation would have instead preferred no one was watching on.

Both fighters were led away from the arena by police, Nurmagomedov forced to leave without his belt as UFC chief Dana White refused to wrap it around the champion’s waist, telling him “If I put this belt on you everyone is going to start throwing s**t.” The projectiles came anyway, drinks and cups raining down on the victor.

This was not a night when it felt like anyone had won, however, least of all the UFC itself.

The build-up to a record-breaking bout had been bitter, but they had happily fuelled that bitterness. McGregor’s criminal acts in Brooklyn in April — when he smashed up a bus carrying Nurmagomedov and other fighters — was the most serious flare-up in a relationship between the pair that has always been fractious.

The UFC, having happily used footage of the incident to heavily promote the fight, reaped what they had sewn.

As the fight approached, things had got even more pointed, more personal. Nurmagomedov insisted on the eve of the showdown that this was more than just a fight. It was personal. There would be no handshakes at battle’s end he said. Too much water had gone under the bridge, too much bile too.

McGregor’s absence from the octagon had lasted almost two years. While he returned talking as good a fight as before, his ability to back up the words once the cage door closed was under greater question than any night in his fighting life.

Facing a champion undefeated as a professional, the Notorious one came in as an underdog. The informed thinking was that Nurmagomedov’s smothering style would prove too much for McGregor if the fight went to the floor or went deeper than a couple of rounds. To regain his lightweight gold, he would have to confound that logic.

The atmosphere inside the T-Mobile Arena had fizzed as Tony Ferguson and Anthony Pettis served up a breathtaking battle in the night’s co-main event. But the Las Vegas lungs still had enough in them for a new crackling crescendo as McGregor strode and then strutted back into the octagon. In the slightly unorthodox role as challenger, he was forced to wait and watch as the champion followed him in.

McGregor landed the first shot of the fight but rarely looked anywhere near his best. He simply wasn’t allowed to. Nurmagomedov was supreme, taking the fight to the ground early in the first and staying exactly there. He was on top throughout and even got the better of McGregor on his feet too. The Russian lands a huge right hand on McGregor’s chin in a second-round, scoring the fight’s only knockdown and bossing a round couldn’t have been more one-sided.

McGregor steadied the ship somewhat in the third, defending the Nurmagomedov takedown attempts and trading blows on his feet. But too few landed true.

In the fourth, the champion put all his skills together to inflict the second surrender of McGregor’s UFC career.

A delicious trip takedown put McGregor on his back again.

The Dubliner would never get upright. With just under two minutes of the round remaining, Nurmagomedov saw his chance to bring things to an end and locked in a rear-naked choke that left McGregor with no option but to submit. The fight was over but the drama was only beginning.

This should have been Nurmagomedov’s finest hour. But he lost his head and lost a world of respect too.

He spotted Dillon Danis, a member of McGregor’s support team, and goaded him, throwing his mouthguard in the American’s direction.

But then he went further, climbed out of the cage and launched himself into the crowd to attack Danis.

The fallout was immediate. Three members of Nurmagomedov’s camp were arrested and led from the arena in handcuffs. The champion will likely have some serious reprimands of his own coming.

There were many lessons on this dark night — for champion and challenger. But the hope is that the UFC will eventually learn some of their own.