Floyd Mayweather Jr (left) throws a left at Andre Berto during their WBC/WBA welterweight title fight at MGM Grand Garden Arena on Saturday in Las Vegas, Nevada. Photo: CFP

Floyd Mayweather Jr cemented his place among the pantheon of boxing greats with a unanimous decision over fellow American Andre Berto on Saturday in what he has repeatedly said would be the final fight of his career.

Mayweather, 38, easily outboxed his younger opponent over the 12 rounds to retain his World Boxing Council (WBC) and World Boxing Association (WBA) welterweight titles and improve his ­perfect career record to 49-0, matching the benchmark set by former heavyweight champion Rocky Marciano.

Five-division world champion Mayweather dominated most of the ­exchanges in the MGM Grand Garden Arena with his lightning jabs, control of space and agile movement about the ring to finish well ahead on all three judges' score cards.

Berto, a 30-1 underdog against one of the best defensive fighters of all time, dropped to 30-4 as he suffered his fourth loss in his last seven fights.

Asked if he might be tempted to come back for a 50th fight, Mayweather replied, "My career is over. It's official. I'm financially secure and I'm in good health.

"I'm close to 40 years old, I've been in this sport 19 years, been world champion for 18 years, I've broken all records.

"There's nothing left to prove in the sport of boxing," said Mayweather, who has made more than $700 million ­during his stellar career.

Back in the ring for the first time since May when he beat Manny Pacquiao in a "mega-fight" that became the richest bout in boxing, Mayweather landed 232 of 410 punches thrown while Berto connected with just 83 of 495.

Mayweather also dominated the jabs count, connecting with 83 of 191 compared to his opponent's paltry 39 of 301.

However, it was a welterweight showdown that failed to capture the public's imagination given Berto's relatively low profile globally and his mixed run of ­results over the past four years, and it was low on entertainment value on the night.

Barely five hours before the start, the MGM Grand box office said "a bunch of tickets" were still available for the arena in the price range between $300 and $1,500, and the official attendance ended up at 13,395 - 3,000 short of full capacity.