Floyd Mayweather won a 12-round majority decision over Marcos Maidana on Saturday to run his perfect record to 46-0 in a welterweight world title unification bout.

The 27-year-old American Mayweather retained his World Boxing Council world title and took Maidana's World Boxing Association belt, winning the fight on two of the three judges' scorecards with the third scoring it a draw.

Mayweather, who was an 11-1 favourite heading into the fight, received scores of 117-111 and 116-112. The third judge scored it 114-114.

Mayweather did not get the decisive victory that so many had predicted as the more aggressive Maidana gave him all he could handle.

Argentina's hard-punching Maidana, who was making the first defence of his title, suffered the fourth loss of his career to go with 35 victories.

Earlier in the Las Vegas evening, Amir Khan showed no sign of ring rust as he made a convincing debut in the welterweight division with a unanimous decision victory over the durable Luis Collazo.

Khan, who last fought in April 2013, was looking to make a statement in the 147lb ranks as he attempts to lure pound-for-pound king Floyd Mayweather into a bout in the future.

And the 27-year-old knocked down the experienced Collazo three times in a near punch-perfect performance on the Mayweather-Marcos Maidana undercard in Las Vegas.

Two judges scored the bout 119-104 while the third had it 117-106 to reflect the dominance of Khan, whose superior hand speed proved the difference in a bout that was for the lightly-regarded WBC Silver welterweight title.