But when the results were announced the pro-Pacquiao crowd booed lustily and tried to drown out Mayweather's post-fight comments over the public address system.
Filipino star Pacquiao suffered the sixth loss of his career to go with 57 victories and two draws.
The fight is widely believed to be the most lucrative in boxing history with revenues of US$400 million.
Floyd Mayweather Jr., celebrates his unanimous decision victory. Photo / AP
Pacquiao was the aggressor, pressing action from the first round and was able to land some big lefts on Mayweather's chin, especially in the final seconds of the early rounds.
But ultimately Pacquiao wasn't able to keep up his frenzied early pace for all 12 rounds and Mayweather, who was the bigger of the two fighters, managed to slip in counterpunches and hard right hands that stopped the Filipino in his tracks.
Mayweather reiterated after today's super fight that he would retire after his next fight in September which will fulfil his six-fight contract to Showtime Sports.
"My last fight is in September. I'll do that and I will hang it up," said Mayweather, estimated to have earned $200 million.
Pacquiao meanwhile insisted he thought he had won.
"I thought I won the fight. He didn't do nothing," he said.
The entrance of the fighters to the ring was delayed about 45 minutes because of problems with the heavy demand for pay-per-view telecast and the providers ability to distribute it.
Manny Pacquiao lands a punch. Photo / AP
Some of the biggest names in Hollywood, entertainment and sports were in attendance, including director Clint Eastwood, actors Robert De Niro, Jon Voight, Denzel Washington, Bradley Cooper, musician Sting, former NBA star Magic Johnson, actress Claire Danes and talk show host Jimmy Kimmel, who visited Pacquiao in his dressing room before the fight.
Only a lucky few had tickets to the super fight but thousands more milled around the outside of the Grand Garden arena and in the hotel's casino.
Before the fight started, the downstairs lobby of the Grand Garden was crowded with people standing about, taking pictures and hoping to catch a glimpse of a celebrity coming in or out of one of the VIP rooms.
Mayweather made a grand entrance befitting of his superstar status. He was accompanied by his "The Money Team" which includes his father/trainer Floyd Mayweather Sr.
But Pacquiao arrived first to the ring, smiling relentlessly and even taking a selfie with long-time trainer Freddie Roach during his entrance.
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- AFP