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As Conor McGregor was humbled once again by Dustin Poirier, Floyd 'Money' Mayweather cashed-in after betting $50,000 on the American to beat his old rival.

The Irishman suffered back-to-back losses for the first time in his career, forced to concede the bout after a gruesome leg-break in the dying seconds of Round 1. 

McGregor's entire legacy hangs in the balance now and Mayweather is revelling in the former double champion's downfall, still holding a grudge from the pair's fiery 2017 boxing match. 

Conor McGregor suffered another defeat in his dwindling career, conceding to Dustin Poirier

Floyd Mayweather bet on his old rival's opponent to win and pocketed a tidy profit on Sunday

The unbeaten boxing champion showed his golden betting slip after Poirier's hand was raised 

The 50-0 icon backed Poirier for victory in the early hours of Sunday morning, and swept up a tidy $35,000 profit from his $50,000 stake. 

Mayweather showed-off his winnings on Twitter, writing: '@dustinpoirier, thanks for getting me paid!' 

The victorious fighter responded: 'I got you champ!'

McGregor has made Mayweather very rich before, with the 44-year-old reportedly pocketing a staggering £270m after his knock-out win over the Dubliner. 

The Irishman bagged more than £100m himself but in the Octagon he hasn't been the same since – losing three of his four subsequent fights. 

Mayweather couldn't help revelling in the victory against his old rival, who he beat in 2017 

McGregor has it all to prove still after back-to-back losses, not looking his best at UFC 264

It's not the first time McGregor has made Mayweather money, cashing-in on their huge bout

The hugely underwhelming face-off was supposed to see McGregor revive his career and setup a clash with Charles Oliveira, after being stunned by a second-round knock-out against Poirier in January, but has only won the Irishman more ridicule. 

The 32-year-old father of three, who predicts he'll be a billionaire in 2023, came out strong with stinging leg-kicks but got caught by Poirier before the American began to dominate on the ground. 

'Mystic Mac's' prophecy was that he'd 'kill' Poirier but after returning to his feet seconds before the end of the opening round and missing a shot, he buckled with a wail as his left leg snapped. 

The former champion went on a rant in his post-fight interview: 'This is not over. If I have to take this outside with him, I’ll go outside. I don’t give a b******s.'

UFC president Dana White also hinted that a fourth fight was on the cards, when it truly will be last chance saloon for McGregor's fighting redemption.