And what it was, without question, was entertainment, as McGregor, the mixed martial artist turned pure pugilist befuddled his experienced foe with an unorthodox style and switch hitting.

But, as ever, Mayweather used the early rounds to figure his opponent out, systematically downloading the data to utilise later in the fight.

And he used it with ruthless abandon, clubbing McGregor, who never once touched down in the fight, onto the brink of oblivion. Referee Robert Byrd put the Crumlin man, boxing competitively for the first time since his teens, out of his misery after 1:10 of the 10th round.

Earlier, Mayweather Promotions fighters Badou Jack and Andrew Tabiti had both recorded victores before Gervonta Davis went off in the co-main event as a 1/40 favourite. The T-Mobile Arena was only about half full when Davis started and the atmosphere was eerily flat.

It was not helped when Davis stopped the tough underdog Francisco Fonseca with a punch to the back of the neck which referee Russell Mora somehow failed to spot. Davis, the burgeoning superstar of Mayweather's stable, was booed loudly during his in-ring interview.

A delay to the main event due to reports of scattered outages from the various cable and satellite providers did not help with generating an atmosphere despite the arena being full.

McGregor had rocked up at the arena about 6pm in a blue three-piece suit flanked by his partner Dee Devlin pushing their baby son, Conor Jr, in a pram. As he made his way to the ring three hours later he looked calm and composed.

Mayweather followed shortly afterwards wearing a balaclava and using around five different rap songs during his 75 metre ring walk. The Las Vegas resident was then booed when his name was read out.

McGregor then made matters worse for the 49-0 by clearly winning the opening round, landing a crunching left uppercut, right-hand combination. Across the planet thousands of people tore up their betting slips which had backed the American to win every session.

McGregor took the second, too, seemingly outfoxing Mayweather by switching stance and throwing lead left hooks. The expectation was always that McGregor would give it a go early on, before Mayweather worked him out and took over.

But by the third round the debutant was even dominating the jab exchanges from both stances and Mayweather looked bereft of ideas as he marched forward holding a high peek-a-boo guard. McGregor, however, had already been warned by referee Byrd for punches to the back of the head in the clinch and he looked unable to resist.

The fourth was a good one for Mayweather, who used his defensive mastery to evade the jab and landed a couple of trademark right-hand counters, which would have reminded McGregor that he was only ever a split second from peril.

The contest was getting scruffy into the fifth but McGregor, used to Brazilian Jiu-jitsu, looked comfortable in the clinch. He was also frustrating Mayweather, who shoved him after the bell to end the fifth.

McGregor had to be hauled off Mayweather by Byrd midway through the sixth after attempting to attack while the American had his back turned. The Dubliner appeared to be feeling the pace but that did not stop him from grinning at Mayweather and putting his hands behind his back, drawing cheers from the almost-capacity crowd.

Despite being 40 years old, Mayweather has not lost any speed with his lead right hand, which he speared a tiring McGregor with ruthlessly throughout the seventh, snapping the visitors head back.

He spent much of the next round back-pedaling as Mayweather walked him down and he needed a series of clinches to catch his breath. The exuberance from those opening rounds was fading badly.

The ninth was pure turmoil for the debutant, utterly exhausted and shipping endless punishment at the hands of the veteran. Somehow he held on to hear the bell but had, by now, fallen well behind on the cards.

But the judges would not be needed as, after just 70 seconds into the 10th, Byrd jumped in to save McGregor's health as Mayweather connected with everything he threw. It was a series of left hooks which finally spelt the end, as McGregor slumped against the ropes.

While McGregor recovered, surrounded by his team and photographers, Mayweather climbed the turnbuckle to celebrate reaching a half century undefeated. After climbing down he moved across the ring and embraced his now 0-1 opponent.

And just like that, the circus was over.