Back in September 2014, McGregor had beaten Poirier inside just two minutes and was the overwhelming favourite going into the rematch as he tries to get fierce adversary Nurmagomedov to reverse his retirement decision.
The American having survived one or two nervy moments early in the first round got his revenge after gaining the upper hand in the second round with some savage kicks to McGregor’s lead leg.
Poirier then forced McGregor into retreat mode with a flurry of punches and eventually flooring him with a short right hook before a couple of blows to the defenceless Irishman led to the end of the fight after two minutes and 32 seconds of the second round.
Watch the highlights of the fight below
McGregor, since October 2018 when he lost to Nurmagomedov had not stepped inside the octagon.
Poirier took down his opponent in the first round but McGregor bounced to his feet landing shoulder strikes that proved so effective in his welterweight victory over Cerrone.
However, Poirier continued to respond with a regular kicking to McGregor’s right calf in an attempt to stifle his rhythm.
It was a tactic McGregor praised afterwards, saying a dead leg meant he “just wasn’t as comfortable as I needed to be” as Poirier capitalised on his opponent’s uneasiness midway through the second round.
“It’s heart-breaking and hard to take,” said 32-year-old McGregor, who turned up to the post-fight press conference on crutches.
“My leg is completely dead. It’s like an American football in my suit at the minute.
“If you put in the time in here, you’re going to get cosy in here and I just have to dust it off and come back and that’s what I will do. I need activity, you don’t get away with being inactive in this business.
“As long as you stay active and as long as you compete, things shape around you. You show up, you reap the rewards. That’s what happened for Dustin and it’s what’s happened against me.
“I’ll keep my eyes on the prize. Don’t write me off yet, I’ll make my adjustments and keep moving. I’ll go back, get healthy and I’ll re-prepare. I’ve got to a great place in my body physically and I’ll continue to grow that.”