During his meteoric rise in the UFC, McGregor has sold his self-confidence with enough flair to turn most anybody into a believer in his invincibility, even in the face of 9 1/2 minutes of contrary evidence.
And when the trash-talking mixed martial arts sensation finally got free late in the second round, he backed up every single word.
McGregor won the interim featherweight title at UFC 189 on Saturday night, stopping Mendes with three seconds left in the second round while emphatically arriving as one of the promotion's biggest stars.
After struggling to break free from Mendes' suffocating wrestling and ground game, McGregor (18-2) finished the fight with a lightning-quick combination after Mendes failed on a submission attempt. A big left hand put Mendes down, and McGregor pounded away for the stoppage before jumping onto the cage in celebration.
"Tonight, I'm going to toast good business," McGregor said. "And it was damn good business. ... It's a crazy game, and you know, I absolutely love it."
McGregor later sank to his knees in tears, an Irish flag in his hands, while the standing-room-only crowd at the MGM Grand Garden Arena roared. The loquacious ex-plumber from Dublin has now made good on just about every boast and threat he ever issued — and there have been thousands.
Mendes (17-3) stepped in for injured featherweight champion Jose Aldo just 2 1/2 weeks ago, and the elite wrestler was in control of the fight until McGregor's heavy hands changed everything in an instant.
Mendes embraced McGregor in sportsmanship after a promotion dominated by high-level trash talk, most of it from a bearded, tattooed Irishman who already looks comfortable with a title belt around his waist.
"I've been hearing all the while that I've been protected from this kind of opponent, that I've been gifted a title shot," McGregor said. "So when my title shot went running and they gave me the challenge I was supposed to be protected from, I (decided) that I'm just going to prove to people that I'm a true fighter."
Robbie Lawler also defended his welterweight title in spectacularly bloody fashion, stopping Canada's Rory MacDonald with a big left hand early in the fifth round. Jeremy Stephens stopped Dennis Bermudez 32 seconds into the third round of a wild brawl featuring multiple knockdowns by both fighters.
But everything on one of the UFC's most entertaining pay-per-view cards was a prologue to the biggest moment yet in the remarkable career of McGregor, who has rocketed through his sport by deploying his sharp tongue as much as his heavy hands.
McGregor has won 14 consecutive fights, and now he has a UFC belt and an enormous future date with Aldo.
"In my opinion, Jose went running," McGregor said. "I had bigger injuries leading up to this fight than that bruised rib, and I still showed up and performed. If he comes back, he can come back, but I swear to God, his day will come."
McGregor and the UFC spent the past several months promoting a title fight with Aldo. McGregor's vocal disdain for the Brazilian and the champion's genuine anger at his challenger's posturing made it an irresistible sell — but the oft-injured Aldo broke a rib while sparring last month.
McGregor was undaunted. He vowed to stay on the card for the thousands of fans travelling to Las Vegas from Ireland, and he agreed to a dangerous bout with Mendes, whose only two career losses were against Aldo.
"He was training for Aldo and got a completely different match, a guy with a different style, on two weeks' notice," Mendes said. "The guy is tough. He talked, but he backed it up."
Before McGregor began his walk to the cage, a small circular stage carrying Sinead O'Connor rose out of a green fog as she serenaded the crowd. Country singer Aaron Lewis did the same for Mendes moments later as the Irish crowd loudly booed.
Mendes cut McGregor above the right eye in the first round. McGregor smiled it off and kept playing to the crowd, but Mendes spent much of the second round on top and in control.
"I was hitting him with everything I had, and the guy was still running his mouth," Mendes said. "That's Conor, I guess. I'd land a giant elbow on his face, and he'd say, 'That's all you got?'"
After Mendes' submission failed, McGregor eventually leaned in to land a right-left combination that stunned Mendes. Referee Herb Dean had to stop it close to the bell.
"I don't have any regrets," Mendes said of taking the fight on short notice. "Conor is a guy that I knew I was going to be fighting eventually. This is the UFC. You have to get in here and do it."
Lawler (26-10) and his Canadian challenger did extensive damage to each other in the penultimate bout. Lawler finally ended his first successful title defence with a big left hand directly into the face of MacDonald (18-3), who rolled onto his back in agony.
Right before that, Stephens and Bermudez put on an amazing featherweight fight. Stephens, who missed weight, bled extensively in the first round, and both fighters were knocked down in a crazy second before Stephens ended it with a flying knee to Bermudez's face.
UFC 189 marked the debut of the promotion's new uniforms. Every fighter walked to the cage and competed in similar outfits designed by Reebok.