Argentina's Carlos Baldomir seized the WBC welterweight title from Zab Judah on Saturday with a 12-round unanimous decision at Madison Square Garden.
The judges scored the bout 115-113, 114-113 and 115-112 for Judah's mandatory challenger Baldomir at Madison Square Garden in New York.
With the upset, Brooklyn-born Judah's WBA and IBF titles became vacant.
Earlier, O'Neil Bell stopped Jean-Marc Mormeck in the 10th round to claim the undisputed world cruiserweight title.
But Baldomir failed to become the undisputed welterweight champion because he never paid the sanctioning fees to the WBA and the IBF.
"Everybody thought this was a unification bout, and no one knew until after the fight that the sanctions were not paid to the WBA and IBF"
Ron Scott Stevens, chairman of the New York State Athletic Commission - which had regulatory authority over the bout at Madison Square Garden, said he was unaware Baldomir had not paid the required fees.
"Everybody thought this was a unification bout, and no one knew until after the fight that the sanctions were not paid to the WBA and IBF," said Stevens.
"Don King announced at the press conference that it was a unification fight," he said. "Everybody thought that was true until after Baldomir made his comments following the bout."
Jamaican-born American Bell, who came into the fight holding the IBF belt, claimed the Frenchman's WBC and WBA titles to become just the second fighter - after Evander Holyfield in 1988 - to unify the cruiserweight crown.
Bell improved to 26-1 with one draw and 24 wins inside the distance.
The 31-year-old appeared to have Mormeck in trouble in the seventh round before dominating from the eighth and finally sending Mormeck down with a barrage of blows at 2:50 of the 10th.
Elsewhere on the undercard, Mexico's Ulises Solis captured the IBF light flyweight title, dethroning American Will Grigsby with a 12-round unanimous decision.
The three judges scored the bout 116-112, 117-111 and 118-110 for Solis, who improved to 20-1 with one draw and 15 wins inside the distance.