Undefeated five-division world champion Floyd Mayweather Jr. weighed in one pound heavier than Andre Berto on Friday, and promised to give the fans "a great fight" in their welterweight title showdown on Saturday.

Though the scheduled 12-round bout at the MGM Grand Garden Arena has failed to capture the public's imagination with heavy underdog Berto having lost three of his last six contests, Mayweather said entertainment would be a priority on the night.

"I'm in top condition, we had a great training camp," Mayweather told a cheering crowd of around 6,000 during an on-stage interview after he and Berto had both been on the scales.

"The main thing tomorrow is going out there, being at my best. Since [Manny] Pacquiao didn't give the fans a good fight, tomorrow is going to be a great fight."

Mayweather will be back in the ring for the first time since he beat Filipino southpaw Pacquiao on a unanimous decision in a much hyped "Fight of the Century" on May 2 that failed to live up to its billing.

Against twice former welterweight world champion Berto, Mayweather is widely expected to win what he claims will be the final bout of his career as he bids to match the 49-0 record of former heavyweight great Rocky Marciano.

"He [Berto] is another tough guy, he has a high knockout ratio, he's a rugged competitor but I've faced everybody in the sport of boxing," Mayweather said after tipping the scales at 146 pounds to deafening roars from the fans.

"I've faced Pacquiao, I have faced [Miguel] Cotto, I've faced Canelo [Alvarez]. I've already faced the best fighters."

Asked whether he was at all concerned that another sporting upset could be on the cards after Serena Williams' shocking tennis defeat earlier on Friday (Saturday NZ time) at the US Open, Mayweather smiled: "I don't overlook any opponent but I've been here before.

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"I know what it takes to win a fight of this magnitude. Just stay focused, stay on a parallel path and go out there and do what I do best, and that's win. I just can't wait to get out there and give the fans excitement tomorrow."

Berto, 30-3 (23 knockouts), tried to inject a bit of needle into proceedings when the two welterweights moved to the front of the stage for the traditional stare-down, crossing his arms in sullen defiance.

"We are here for a reason," Berto, 32, said when asked to explain his tactics. "I don't get caught up in all the rest of it. I already been through a lot and ... on Saturday night we're going to go in and do what we do."

As for being a 30-1 underdog against Mayweather, 48-0 (26 KOs), Berto was totally unphased.

"It don't matter. Where I come from, we never had a chance to come out of that," said Berto, who was regarded as a 'problem child' by his parents before being taken to the gym as a 10-year-old by his father to learn discipline.

"Just the fact that I'm here tells you something."