Floyd Mayweather Jr added the WBA Super World light-middleweight title to his supreme career roster with a battling unanimous points victory over Miguel Cotto in Las Vegas.

Mayweather, fighting at the 154lbs limit for the first time since defeating Oscar De La Hoya to win the WBC belt exactly five years ago, won favour by margins of 118-110 and 117-111 (twice) on the judges' scorecards to preserve his unblemished 43-fight record.

Defending champion Cotto slips to 37 wins and three defeats as a professional.

Attentions will once again turn towards the prospect pairing Mayweather with pound-for-pound rival Manny Pacquiao, but the 35-year-old American must first serve a three-month prison sentence after pleading guilty to a domestic violence charge.

Mayweather's crisp left jab was the defining feature of the opening round, while the challenger showed he was willing to trade at close quarters as Cotto increased the pace and physicality of the contest in round two.

By the fourth Mayweather was starting to unfurl the whole repertoire and a stinging left uppercut momentarily buckled the champion's legs.

Cotto landed a meaty left hook in round five as he relentlessly burrowed forward and the 31-year-old Puerto Rican enjoyed his best three minutes to date in round six, drawing blood from the nose of his opponent who appeared to be feeling the relentless pace.

An absorbing ebb and flow continued across the subsequent two sessions, as Mayweather's slick backfoot work gave way to another dose of Cotto's frenetic pressure.

The champion managed to impose his style down the stretch, regularly pulling Mayweather out of his comfort zone and into the trenches.

But Mayweather's dazzling defensive and counter-punching skills came to the fore in the final two rounds, as he sealed an eighth world title across five weight divisions.

Speaking to US broadcaster HBO after the fight, Mayweather stated his desire to face Pacquiao next and suggested the bout might have already taken place but for the presence of the Filipino's promoter, Bob Arum.

"This fight right here, I was looking to fight Manny Pacquiao," he said.

"The fight didn't happen, I don't think the fight could happen because of Bob Arum.

"Bob Arum was in the way - he stopped the Pacquiao fight.

"Let's give the fans what they want to see. They want to see Mayweather-Pacquiao."