Las Vegas, Sep 13 (AFP) Floyd Mayweather earned a unanimous decision over Andre Berto to claim his 49th and he says final victim in a glittering unbeaten ring career spanning two decades.

All three judges ruled overwhelmingly in Mayweather's favor and afterwards the American welterweight world champion confirmed that he was retiring, saying: "My career is over.

"It's official."

He equals the perfect 49-0 record of heavyweight legend Rocky Marciano and retains his WBA and WBC titles, embellishing his reputation as the best boxer of his generation.

Mayweather fell to his knees in the ring after the bell, taking in the moment.

"I want to thank all the fans... for 19 years I would not be able to do it without these fans," he said, after the judges ruled it 118-110, 117-111 and 120-108, all to the champ.

"But you have to know when it's time to hang it up. I'm knocking at the door; I'm nearly 40 years old now.

"There's nothing else to prove in the sport of boxing.

I'm leaving the sport with all my faculties; I'm still sharp and smart."

The 38-year-old self-styled "TBE" ("The Best Ever"), who had consistently said that the Berto showdown would be the last time he steps into the ring, had too much guile and nous for the rank outsider.

Berto, who has now lost four of his last seven fights, was set up as the fall guy for the pound-for-pound king's coronation -- and he played the role perfectly, showing plenty of heart but not quite enough quality.

Mayweather has his critics, but he was given a hero's welcome at the MGM Grand Garden Arena in Las Vegas by a boisterous crowd who had come expecting to see him give Berto, 32, an old-fashioned shellacking.

He did not quite do that, but instead used his sublime defensive skills to avoid the worst that Berto -- a former two-time world champion -- could throw at him.

Berto kept coming at Mayweather; Mayweather would land a quick-fire combination and then dart out of trouble again -- to roars of approval for the man fans have taken to calling simply "Money."

Even when he had Mayweather against the ropes Berto found it hard to connect with anything meaningful.

The first real taste of a fight breaking out came at the end of the second round, when the two tangled after the bell, Mayweather giving his foe a dirty look.