Hatton, the challenger, was two pounds (907 grams) lighter at the weigh-in held at the MGM Grand Garden Arena, the site of Saturday's bout, in front of a crowd of 6,000 almost exclusively British fans.
The two fighters stood nose-to-nose after the weigh-in with Hatton waving the American away as he took the microphone to tell his fans: "What can I say for a turnout like that?"
Members of the raucous crowd, who sang football chants plus several renditions of 'God Save the Queen' and 'There's only one Ricky Hatton', had queued for up to five hours for a chance to catch a glimpse of the fighters at the weigh-in on Friday.
"I just think Ricky's in the best shape he's ever been in."
Joe Calzaghe, world super middleweight champion
The 16,800-seat arena sold out within 30 minutes of tickets going on sale for the fight in September and internet resale sites are offering ringside seats for almost $13,000.
More than 10,000 British fans were expected to make the journey to watch the showdown at the arena or at one of several closed-circuit venues along the Las Vegas strip.
Mayweather, who has a 38-0 win/loss record, is widely regarded as the best pound-for-pound boxer in the world but Oscar De La Hoya, who was the last man to fight him, believes underdog Hatton, 43-0, has a strong chance of winning the fight.
"People are underestimating (Hatton's) speed and his footwork," De La Hoya, who is promoting the bout, told reporters.
"He has to keep popping that jab. You know he's not going to tire out. He's going to keep that fast pace for twelve rounds."
Fight could be 'a war'
Mayweather beat De La Hoya by split decision in the same arena on May 5, in the highest-grossing fight in history.
Joe Calzaghe, Britain's undefeated world super middleweight champion, said he believes the fight "is going to be a war".
"I just think Ricky's in the best shape he's ever been in," Calzaghe told Reuters.
"I think he wants it more than Mayweather.
"He can't outbox Floyd, he can't stand off from a distance. He has to jump on him early.
"It is very important that in the first four rounds he stamps his authority, maybe hurts Floyd, and gets him out of his rhythm."
Mayweather is a six-time champion in five different weight classes.