Conor McGregor celebrates after defeating Chad Mendes during their interim...

Conor McGregor celebrates after defeating Chad Mendes during their interim featherweight title mixed martial arts bout at UFC 189 on Saturday, July 11, 2015, in Las Vegas. Credit: AP / John Locher

Conor McGregor backed up every single word.

The Irish mixed martial arts sensation won the UFC interim featherweight title at UFC 189 on Saturday night, stopping Chad Mendes with three seconds left in the second round with a vicious series of strikes.

McGregor (18-2) spent much of the first two rounds on his back, but he finished the fight with a lightning-quick combination soon after he reached his feet. After a big left hand put Mendes down, McGregor pounded away for the stoppage and then jumped onto the cage in celebration.

McGregor later sunk to his knees in tears while thousands of Irish fans at the MGM Grand Garden Arena roared in adoration of a loquacious fighter who can make good on every boast and threat.

"To come in here and hear all this applause, it's just amazing," McGregor said. "I truly appreciate it."

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 the pugnacious Irish brawler 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. It doesn't matter who it is, I'll show up and I'll put a finish on any 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, highlighting an action-filled pay-per-view card.

But everything was a prologue to the biggest moment yet in the meteoric MMA rise of McGregor, the former plumber from Dublin 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.

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 the Irish challenger's posturing made it an irresistible sell -- but the oft-injured Aldo broke a rib while sparring.

McGregor was undaunted. He vowed to stay on the card for the thousands of fans traveling to Las Vegas from Ireland, and he agreed to a dangerous bout with Mendes, a vicious wrestler whose only two career losses were against Aldo.

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.

The fighters exchanged trash talk and posturing before and after the opening bell, but Mendes landed the first major strike when he 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 of McGregor as the crowd booed.

Mendes again got top control in the third, but McGregor escaped late in the round -- and his pugilistic prowess decided it. McGregor leaned in to land a right-left combination that stunned Mendes, and McGregor pounced with blows on his prone opponent until referee Herb Dean had to stop it three seconds before 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 MacDonald did extensive damage to each other in the penultimate bout, and Lawler's Canadian challenger ended up with a badly damaged nose. Lawler finally ended it with a big left hand directly into the face of MacDonald (18-3), who rolled onto his back in agony before Lawler finished him 60 seconds into the fifth.

The crowd was fired up for the title bouts by Stephens and Bermudez, who 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.

Icelandic welterweight Gunnar Nelson (14-1-1) also finished Brandon Thatch in impressive fashion midway through the first round, flooring Thatch with a combination before sinking a choke.

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. The shorts feature their names, a Reebok logo and theoretically nothing else, now that individual sponsors are banned -- although MacDonald's trunks still had a logo for an energy sports drink.

More MMA