Argentina's Marcos Maidana outpointed Mexico's five-time world champion Erik Morales on Saturday to claim the WBA interim light-welterweight title.
Two judges scored the bout 116-112 in favour of the 27-year-old Maidana and the other had it 114-114.
Maidana, who was defeated by Britain's Amir Khan on points in December, felt he was good value for the win.
"This was my toughest fight yet," he admitted. "It was close but I came on strong in the end and deserved to win."
Maidana started the fight well, dominating his slower and older opponent in the first few rounds. Morales' right eye was swollen shut by the end of the second round, handing Maidana the advantage.
The 34-year-old Morales, a heavy underdog, looked well past his prime in the early rounds, but rallied in the middle rounds to keep the fight close.
Despite tiring as the fight went on, the more aggressive Maidana found a second wind and enjoyed the better of the last two rounds before clinching a narrow victory.
"I knew it would be difficult so I trained hard and was prepared," said Maidana, who improved to 30 wins from 32 fights.
Morales, however, was not convinced it was a legitimate result, claiming he had the better of the fight.
"Maidana may have won a close fight but it wasn't a clean win for him," said Morales, who dropped to 51 wins and seven defeats.
"I thought I landed the better punches. I thought I won. I know I still had speed and velocity, but more importantly I had heart."