With the blows raining down on McGregor he should have taken an eight count and perhaps prolonged Mayweather’s 50th bout.
But he courageously refused to meet the canvas and was instead rescued by referee Robert Byrd before he was seriously hurt.
Mayweather was roundly booed during his lengthy introduction. The boxing icon looked nonchalant as Byrd gave his final instructions.
The Irishman maintained a steely gaze but Mayweather was almost pulling faces like a naughty child.
McGregor went straight to work, firing that long left hand into the Money Man but only pounding away at his arms.
The Irishman’s movement was nothing extraordinary and he needed just 90 seconds to mock the unbeaten icon by folding his hands behind his back and offering up his luxuriously-bearded chin.
McGregor was looking for a big body shot early on, to test the abs on the 40-year-old.
The UFC hero was warned at the start of the second for rabbit punches to the back of the head, the same illegal shots he peppered ex-sparring partner Paulie Malignaggi with.
Three times in the second round the pair clashed in the clinch but there were no signs of any roughhouse tactics from the MMA hero.
The Dubliner was expected to use the close encounters to target Mayweather’s elbows and shoulders but there was no wrestling or armbars used.
McGregor tried switch hitting in the third, swapping lead leg in an effort to unsettle Pretty Boy but it didn’t work as he settled in for the night.
In round four there was a couple of rare meaningful punches thrown by both men, their chins held up under scrutiny.
Mayweather lost his cool at the end of the fifth round after another slow round.
The boxer shoved McGregor in the chest well after the bell and was warned by referee Byrd who was busy again in the sixth when McGregor was warned again for illegal punches.
The 29-year-old was caught with a barrage of right hands from Mayweather and the younger man seemed to be breathing heavily and his face was begining to mark from the punishment he was suffering.
And the seventh offered him no respite with Mayweather thoroughly out of his two-year retirement and throwing bombs.
McGregor answered any questions about his chin with a Spartan resilience.
But the ninth was McGregor’s nadir, he was swatted all over the ring by his rival, beaten from corner to corner, he clung on for the dear life, wrapping his long arms around the 49-0 star and somehow remaining vertical.
But in round 10 the Money Man cashed in by battering the brave martial artist senseless until Byrd flew in.
Elsewhere on the bill, Nathan Cleverly was stopped by Badou Jack in the fifth round of their WBA light heavyweight clash.
Mayweather protege Gervonta Davis, meanwhile, beat Francisco Fonseca in the eighth round in a bout that was supposed to be for a world title before Davis missed the weight.
Mayweather said: “I told you the fight would be blood, sweat and tears and that’s what I gave you.
“I owed the fans for the Pacquiao fight. I cam straight ahead and gave the fans a show.
“Hes a lot better than I thought he was. He’s a tough competitor but I was the better man tonight.
“Our game-plan was to take our time and take him down the stretch. We wanted him to shoot heavy shots in the beginning. In the MMA he fights 25 mins really hard but then starts to slow down.
“This was my last fight tonight. I chose the right dance partner to dance with. Conor McGregor is a great champion.”
A beaten McGregor said: “He’s not that fast or powerful but boy he’s composed in there. I have to give him respect for the great career hes had. F**k it I had a bit of fun over here.
“Early on I felt handy enough but he was composed in there and fair play to him. That’s what 50 pro fights does for you.
“There’s a lot on the line here. The ref should’ve let me keep going. I was just a little fatigued.
“I get a bit wobbly when I’m fatigued, that’s why I thought the ref could’ve just let me go on and let me go down.
“In the final two rounds you got to let me go back to the corner and wobble it out.”
The total revenue is set to smash the £500million barrier as Sky Sports won the battle with BT Sport to show the fight in the UK and the bout will be on pay-per-view in the US.
Mayweather is expected to pocket around £78.5m, or $100m if you’re from across the pond.
Not bad for a night’s work.
But as Mayweather is co-promoting the event in with the UFC, he is hoping to earn over £230m from the event.
