Back in 2015, McGregor was on the verge of becoming a breakout star in the UFC, with his cocky attitude and exciting style of fighting proving immensely popular with the MMA fanbase.
But when he came up against Mendez, he seemed to have met his worst possible matchup at least on paper.
A two-time NCAA Division I All-American, Mendez is widely regarded as one of the best wrestlers in mixed martial arts.
Fighting out of Sacramento, California, he spent his entire career training at Team Alpha Male before retiring from MMA in 2018.
Prior to that fight, he had won four of his last five fights including knockout victories over Darren Elkins and Ricardo Lamas.
McGregor, meanwhile, was on a 13-fight winning streak stretching back to November 2010.
He was originally supposed to challenge then-UFC featherweight champion Jose Aldo for the title at UFC 189, but after Aldo was forced out due to injury, he faced Mendez for the interim 145lbs belt instead.
WATCH: Conor McGregor knocked out Chad Mendes at UFC 189
Check out the video below…
User @TheArtofWar6 posted a short highlight clip from the fight and wrote: “Conor McGregor was just unstoppable back then.”
The video has been retweeted more than 1,400 times, liked by almost 21,000 people and viewed a staggering 822,000 times.
McGregor spent a significant amount of time on his back due to Mendez’s four takedowns but targeted his body with a variety of different kicks.
And it wasn’t long before those body shots began to take their toll as Mendez visibly started to slow down in the second round before eventually being stopped with strikes shortly before the bell.
And according to McGregor’s coach John Kavanagh, everything went exactly according to plan.
Speaking on Sky Sports in 2015, he said: “It was extremely obvious to me that Chad was getting very tired.
“He hit a few high-aptitude throws which look great but they cost him a lot of energy. He then expended a lot of energy just trying to hold Conor to the ground.
“If there’s one thing you’re never going to do, it’s tire Conor out. It was obvious to me that Chad was breaking slowly. I knew that, even if he managed to get through the second round, he would never have got through the third because he was too tired.
“Twenty-five minutes is a long time to be locked inside a cage with Conor McGregor.
“It was nothing to do with being a short-notice replacement – he is a professional athlete who will not get tired after a few minutes’ work. That’s not how it works. Chad could have had a two-year training camp but he would have been tired quickly because Conor was hurting his body.
“In the boxing world, it’s well known what body shots can do but in MMA they’re not used enough.”