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.