Boos rang out from a pro-Pacquiao Las Vegas crowd as Mayweather’s emphatic victory was confirmed by all three scorecards after 12 rounds of cat and mouse action.

Mayweather comfortably outboxed his Filipino rival to snuff out any chance of the full-blooded slugfest that the more aggressive Pacquiao was hoping to ignite.

The win extended Mayweather’s remarkable 19-year unbeaten record to 48-0, putting him within one fight of equalling Rocky Marciano’s legendary milestone of 49-0.

The 38-year-old Mayweather retained his World Boxing Council and World Boxing Association welterweight titles and seized Pacquiao’s World Boxing Organization belt by winning the fight on all three of the judges’ scorecards.

‘‘He’s a very awkward fighter, so I had to take my time and watch him close,’’ Mayweather said. ‘‘All 47 fights before I got to this fight played a major role in my career.

‘‘Manny Pacquiao is a true champion and we both did our best tonight. When the history books are written, this fight will have been worth the wait.’’

The fight is widely believed to be the most lucrative in boxing history with revenues of $US400million ($506million).

Ringside judge Dave Moretti scored the bout 118-110 for Mayweather, while judges Glenn Feldman and Bert Clements both scored it 116-112 for the American. 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. Their Filipino star Pacquiao suffered the sixth loss of his career to go with 57 victories and two draws.

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 kept the Filipino southpaw at bay.

Even so, Pacquiao said he thought he did enough to earn the victory.

‘‘I thought I won the fight,’’ he said. ‘‘He didn’t do nothing.’’

Mayweather reiterated afterwards that he plans to 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. 

He is estimated to have earned $US200million ($253million) for one night’s work. Pacquiao will receive well over $US100million ($A126million) in a 60-40 purse split the fighters agreed to beforehand.

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 and talk show host Jimmy Kimmel, who visited Pacquiao in his dressing room before the fight.

The tension in the ring was also intense as the fighters exchanged words and even traded low blows in the third round.

In the fourth round Pacquiao landed his best punch of the fight to that point, hitting Mayweather with an overhand right that knocked him back to the ropes.

He then added a flurry of punches for good measure as the crowd screamed like crazy for him to end the fight.

A couple of times Pacquiao had Mayweather on the ropes but the superbly-fit American took everything he could dish out and still had enough energy in the later rounds to jab, connect with some overhand rights.

He deftly moved out of harm’s way each time Pacquiao came in close for the knockout punch.