Manny Pacquiao was less than half a kilogram lighter than Floyd Mayweather when they weighed in on Friday for their fight in Las Vegas.

The pre-fight ritual drew a stunning crowd of 11,500 to the MGM Grand Garden Arena. Tickets were sold at $10 each but some paid much more on the secondary market for a chance to see two of the most talented fighters of their generation step on the scale.

"It is an unbelievable turnout," Mayweather said. "I am glad all the fans came out to support myself and support Manny."

Pacquiao said he saw something in Mayweather's eyes that reinforced his belief that he would be the first to defeat the American.

"I saw a man with a lot of worries," he said after the stare-down.

While a relaxed-looking Pacquiao beamed at his followers, Mayweather kept his game-face on.

"My thing is to focus on what we've got to do tomorrow," Mayweather told the crowd. "I've dedicated myself to the sport of boxing for more than 20 years, and I'm ready."

Earlier in the week he said: "I never wanted to win a fight so bad in my life."

Pacquiao’s fans made their presence felt, with loud chants and even a few boos for Mayweather.

Bookmakers were taking big wagers on Mayweather but the money coming in from Pacquiao’s backers had narrowed the odds to about 2-1 in Mayweather's favour.

A deafening roar went up when the two champions stood face to face in a brief stare-down at the front of the stage.

"Pacquiao is going to win in the sixth round because he just has so much aggression about him," said Adam Reed, who had flown in from London.

Fans of the Filipino wore a variety of costumes, including three Filipino nurses from Miami who wore yellow Pac-Man video game outfits.

"Pacquiao is going to come out fast and win the first six rounds," said 40-year-old Michelle Lakibul. "Mayweather will win four rounds in the middle but Manny will come on later and win the fight by a decision."

Pacquiao was relaxed and smiling, even thanking Mayweather on stage for helping make it happen. "I believe the fans deserve this fight. They deserve a good fight," Pacquiao said.

When it was Mayweather's turn to climb up on stage he appeared all business as he gazed out at the crowd.

Boxing fan Frank Pino, of Phoenix, Arizona, said he was betting on Mayweather to win on points.

"Look at his past performances," said the 32-year-old. "He plays with opponents early on then takes it in the later rounds."

But some die-hard Pacquiao fans were not sure their hero was going to win. "Like everybody else my heart is with Pacquiao but Mayweather will win," said George Tavarez, 34, of Yakima, Washington. "Floyd is too smart and he has a perfect game plan."