LAS VEGAS – Juan Manuel Marquez weighed in four pounds lighter than American Floyd Mayweather Jr. as the Mexican was greeted by deafening cheers from passionate fans on the eve of Saturday's non-title welterweight fight.

Five-times world champion Marquez, 50-4-1 (37 knockouts), tipped the scales at 142 pounds (64kgs) in front of a boisterous crowd of around 1,500 at the MGM Grand Hotel's Garden Arena.

Mayweather, 39-0 (25 KOs) and a heavy favorite to win at his natural weight, registered a surprising 146 pounds (66 kgs) after being booed by the largely Hispanic supporters.

When the eagerly anticipated fight was first announced in May, it was described as a welterweight bout with a catch weight limit of 144 pounds.

However Golden Boy Promotions chief executive Richard Schaefer told reporters on Friday weight penalties had been added to the contract in case either fighter came in too heavy.

With Mayweather exceeding the limit by two pounds, Marquez would benefit financially, Schaefer said.

"All parties signed the agreement and he (Mayweather) will have to come up with a substantial amount of money," he added while refusing to disclose the figure.

No surprise

"Sometimes size matters, and sometimes size doesn't matter. But it was all contractually dealt with ... so it was no surprise to Marquez and it was no surprise to Mayweather."

Marquez, who has moved up two weight classes to challenge Mayweather, has never fought above 135 pounds and could be at least 10 pounds lighter than his opponent when the duo enter the ring on Saturday.

"A lot of people think (I can't win) because of the weight," the 36-year-old Mexican said. "But I have trained very hard on my strength and my muscles. I feel good.

"I have my mind, I have my concentration and I have the motivation to win. This fight is the most important of my career."

The atmosphere in the Garden Arena was electric as the two fighters made their way on to a raised stage for Friday's televised weigh-in where former world champions Thomas Hearns, Oscar De La Hoya and Bernard Hopkins were among those attending.

The Marquez fans drowned out Mayweather's supporters, repeatedly singing "Ole, Ole, Ole, Ole ... Marquez, Marquez" and "Viva Dinamita," referring to the Mexican's nickname.

Mayweather, who returns to the ring after a 21-month absence, resorted to strutting and posturing around the stage after arriving for his introduction wearing a hooded tracksuit.