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McGregor might have been out of action for just over a year before getting in the octagon at UFC 257 but most people expected the Notorious to come out on top.
The Irishman tapped into his usual 'Mystic Mac' ways to predict that he would stop the Diamond in the first round, in what would have been a repeat of their first fight.
Even Khabib Nurmagomedov agreed, claiming McGregor would win early or Poirier would win late, but everyone got it wrong.
Instead it was the American who was the victor, stopping the Irishman in the second round to become the first man to cause a TKO loss for McGregor.
That was certainly good for one fan who placed a $200,000 bet on Poirier to win at odds of around 2.7/1, meaning a return of $740,000, or £541,000.
Another punter did pretty well for himself with a bet of $100,000 at the same odds, certainly a good night for the pair of punters.
McGregor started fast in their first fight in 2014 and he tried the same tactics in Abu Dhabi on Saturday night, but Poirier was determined not to go down the same way again.
The Diamond scored a takedown early in the first round but McGregor defended well to get back to his feet and did well in the clinch.
He had the better of the latter part of the round but Poirier continued to land leg kicks to his opponent's calf.
Those kicks inevitably did it for the American as the former lightweight champ McGregor couldn't cope with them and Poirier eventually finished the fight with punches.
Poirier's win puts him in touching distance of winning the lightweight title, or at least competing for it, but it probably won't be against current champion Khabib.