Shane Mosley gained a controversial points win over Oscar de la Hoya to become the WBC and WBA super welterweight champion in Las Vegas.
All three judges awarded the fight to Mosley by the score of 115-113.
But De la Hoya controlled the pace for large chunks of the fight, outboxing Mosley as he looked for revenge for his June 2000 loss.
British boxing commentators Ian Darke and Glenn McCrory had De la Hoya winning the bout by a huge margin, as did former world champions Barry McGuigan and Jim Watt.
De La Hoya, in front of a star-studded crowd which included Tiger Woods, Lennox Lewis and singer Christina Aguilera, dominated the fight according to punch statistics, outlanding Mosley 221 to 127 overall.
But crucially, Mosley was awarded each of the final five rounds.
De la Hoya, 30, vowed afterwards to fight the decision.
He had been rocked in the fifth, ninth and 12th rounds, but his superior jab and speed kept Mosley at bay.
Despite suffering a cut at the start of the fourth from an accidental clash of heads, De la Hoya stayed composed and continued his gameplan of circling the ring and peppering Mosley's head with jabs and right hands.
But from rounds eight through to twelve, De la Hoya's pace slowed and Mosley came back into the contest.
De la Hoya may now retire
The 32-year-old was being implored by his trainer and father Jack to fight harder and he seemed capable of stopping De la Hoya in the ninth when a huge right hand to the body seemed to take the wind out of the champion.
Mosley landed a huge right hand in the final round and at the final bell, the pair embraced, with neither confident they had done enough to win.
The beaten champion refused to state whether he would carry out his pre-fight intention of retiring if he lost.
"I thought I won the fight. I didn't think it was even close. I thought I won by at least three points," said De la Hoya.
Naturally, Mosley disagreed.
"I thought it was a very close fight...but I felt much stronger than De la Hoya," said the new champion.
Mosley recorded his second win over De la Hoya, having beaten him for the WBC welterweight title in 2000.
It was De la Hoya's third defeat in 39 fights, while Mosley made it 39 wins from 42 fights, with two defeats and one no-decision.