Irish star McGregor -- who had been accused by Mayweather of struggling to make the 154-pound limit -- weighed in comfortably at 153 pounds in a raucuous face off at the T-Mobile Arena.
McGregor heavier for Mayweather showdown
Mixed martial arts star Conor McGregor will carry a sizeable weight advantage into his superfight with Floyd Mayweather after tipping the scales nearly four pounds heavier than the boxing legend here Friday.
Former welterweight king Mayweather, 40, meanwhile came in at 149.5 pounds.
McGregor, 29, is likely to bulk up substantially before Saturday's 12-round bout, meaning Mayweather will be several pounds lighter than the two-time UFC world champion.
"That's the worst shape I've ever seen him in. Trust me on that," McGregor roared after the weigh-in.
"I'm a professional, I make weight, that's dedication, that's focus. I'll be a lot bigger than him tomorrow, closer to 170," he added.
A nonplussed Mayweather meanwhile shrugged off his likely weight disadvantage and once again vowed to stop McGregor inside the distance.
"I've been here before. I know what it takes for a fight of this magnitude," Mayweather said.
"Weight doesn't win fights, fighting wins fights. It won't go the distance. Mark my words -- I'm not worried about the scales."
A rowdy crowd of around 6,000 fans thronged the arena for Friday's weigh-in in a sign of mounting anticipation for the fight that has captured the imagination of the combat sports world.
Mayweather is returning to the ring two years after retiring from the sport with a 49-0 record.
A 50th victory against McGregor on Saturday would take the former welterweight world champion one clear of heavyweight legend Rocky Marciano.
McGregor, the two-time Ultimate Fighting Championship world champion, will start as a massive underdog in what will be his first professional boxing fight.
Although widely seen as a mismatch between the novice McGregor and the vastly more experienced Mayweather, the fight has generated massive excitement and could become the most lucrative bout in history.
Mayweather could earn as much as $200 million from the contest if pay-per-view television targets are met, while McGregor's share of the purse could reach $100 million.
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