McGregor vows Mayweather knockout as moment of truth nears

Las Vegas : Mixed martial arts star Conor McGregor vowed to knock out boxer Floyd Mayweather on Friday as a horde of Irish fans descended on Las Vegas for the trash-talking rivals' cross-combat super-fight.

McGregor, 29, will carry a substantial weight advantage into Saturday's 12-round boxing contest at the T-Mobile Arena after a raucous weigh-in that saw him face-off with Mayweather for the final time before fight-night.

With waves of green-shirted fans in a crowd of around 6,000 roaring their support for the Irish superstar, McGregor tipped the scales at 153 pounds, well inside the 154-pound limit.

Former welterweight champion Mayweather, 40, who has emerged from a two-year retirement to take on MMA star McGregor, weighed in at 149.5 pounds.

The naturally bigger McGregor -- who screamed into Mayweather's face as the two men went nose-to-nose -- said he expects to enter the ring at closer to 170 pounds.

Saturday's one-off bout is projected to be the richest fight in history, with Mayweather poised to earn as much as $200 million and McGregor potentially pocketing around $100 million.

McGregor, who has never fought in a professional boxing contest, is a massive underdog for a fight, which is expected to beamed live to around 200 countries and territories across the globe.

But the former apprentice plumber from Dublin, who was unemployed four years ago, defiantly predicted he was ready to spring a monumental upset on the skilful Mayweather, one of the finest boxers in history who boasts a perfect 49-0 record.

"That's the worst shape I've ever seen him," McGregor said of Mayweather. "I'm going to breeze through him, trust me on that."