Floyd Mayweather outpointed a game Marcos Maidana in Las Vegas to unify the welterweight division and remain unbeaten in 46 professional fights.
Mayweather, who is now the WBC and WBA champion, was the red hot favourite but Maidana showed tremendous commitment and dominated the early exchanges.
But having weathered the Argentine's thunderous start, American Mayweather assumed control in the middle rounds.
One judge scored the fight 114-114, the other two 117-11 and 116-112.
It was judge Michael Pernick's card which made the outcome of the fight a majority rather than a unanimous decision, but his verdict seemed greatly at odds with what had transpired.
Maidana protested he had been cheated and called for a rematch, which Mayweather appeared to agree to. In truth, Mayweather was in a different class for most of the contest.
Five-weight world champion Mayweather, 37, has three fights left on his contract with American television network and will fight next in September.
The 30-year-old Maidana, who was outpointed by Britain's Amir Khan in 2010, started like a train, assailing Mayweather with a salvo of chopping right hands in the opening round and landing with some of them.
Mayweather found his range in the second, landing with a couple of cute right hands and sneaky left hooks as Maidana continued to march forward.
Maidana had Mayweather on the ropes again in the third and while the American was making most of his rival's punches miss, the Argentine was having some success to the body.
The roughhouse Maidana opened up a cut over Mayweather's right eye in the fourth, although it might have been via an accidental clash of heads rather than his fists.
And while Mayweather landed with a spiteful uppercut towards the end of the round, Maidana could well have edged it on superior work-rate.
Mayweather looked rattled on his stool before the start of the fifth, complaining that he was unable to see because of blood trickling into his right eye.
And Maidana landed with a wicked right midway through the fifth as Mayweather continued to look strangely confounded.
However, Mayweather landed with some classy shots in round six, including a wicked right uppercut and a peach of a right cross.
Round seven was confirmation that the tide had turned, with Maidana showing less intensity and Mayweather landing with some crisp shots.
But Maidana continued to bulldoze forward in the eighth, roughing his rival up on the ropes and possibly trumping Mayweather's classier, but less frequent, shots on the counter.
Mayweather finished the ninth round strongly, snapping Maidana's head back with a couple of sharp overhand rights and stopping him in his tracks with a right to the body.
Maidana showed real signs of tiredness in the 10th and Mayweather took advantage, strafing his opponent with looping rights to the head and body and he continued to land the cleaner shots in the penultimate round as Maidana's work began to look a little desperate.
However, Maidana came on strong in the final round but Mayweather had already done more than enough to win the fight.
Mayweather has now only stopped one opponent in seven years but is undefeated since making his professional debut in 1996.
Maidana, meanwhile, has 35 wins and four losses from 39 pro fights and remains a major player in and around the 147lb division.
On the undercard, Adrien Broner bounced back from his defeat by Maidana last December with a unanimous points victory over fellow American Carlos Molina.
The win for the 24-year-old, who has 28 wins and one defeat from 30 fights, puts him back in the frame as a future Mayweather opponent.