Fighting for the first time in a year, McGregor was looking to restore himself back into lightweight title contention and ultimately set up a rematch against bitter foe Khabib Nurmagomedov.
But things did not go according to plan for the Dubliner as Poirier dismantled McGregor with a second-round assault, rocking his rival with a big left hand against the cage before following up with a barrage of strikes to send McGregor to the canvas and end the contest.
It was revenge for Poirier, who had lost the pair’s first fight inside the first round back in 2014.
McGregor had arrived on Fight Island in typically ostentatious style, sailing in on a super yacht as the former two-weight champion stated he was back to reassert himself as the king of the 155lbs ranks.
But despite the showdown with Poirier carrying all the pomp and hype of a Conor McGregor bout, it lacked the fireworks the Irishman has shown so often in the octagon down the years.
The first round at the Etihad Arena did not see the first-minute knockout that ‘Mystic Mac’ had predicted, with a cautious opening as both fighters kept their distance.
Poirier secured an early takedown but McGregor recovered as the pair spent much of the round up against the cage.
In the clinch, McGregor worked the shoulder again, just as he had done to such devastating effect against Donald Cerrone in his last contest.
Once back in the open, the Irishman’s striking skills came to the fore as he landed a series of clean shots on Poirier to edge the first round.
But it was a different story in the second stanza as Poirier had more success with his calf kicks before setting up a brutal finish with a big left hand, rocking McGregor against the cage. A further barrage from Poirier ended the fight with McGregor stricken on the mat.
It was the first non-submission defeat of McGregor’s career and his second loss in his past three fights.
For Poirier, it was sweet revenge for his defeat to the Notorious in 2014 and means the former interim lightweight champion moved himself firmly back into title contention.
In keeping with the respectful tone to the build-up of the fight, a “gutted” McGregor used his post-fight interview to praise Poirier but also point to inactivity as one of the factor’s behind his defeat.
The defeat almost certainly means McGregor can kiss goodbye to his chances of ever running it back with Khabib, who had supposedly said it would take something “spectacular” to tempt him out of retirement for one final fight.
McGregor signaled he would dust himself off for further contests in 2021, but he is now contemplating a far lengthier route back to the top, should he ever get there.
In contrast, Poirier laid out his credentials for a shot at the 155lbs title, should it ultimately be vacated by Khabib as many expect.
Poirier’s next opponent could be UFC newcomer Michael Chandler, who scored a spectacular knockout win of his own in the co-main event on Fight Island, finishing Dan Hooker inside the first round of their contest.
It was a stunning UFC debut for the three-time former Bellator champion, who could now be set for a lightweight title scrap with fellow victor Poirier.