Byrd won the vacant IBF title last December

Oquendo criticised the judges' verdict, which was booed by the Connecticut crowd.

"The judges once again shafted another great fighter," said the 30-year-old.

"He hardly hit me, I was the aggressor."

It was the southpaw's 37th win in 39 bouts and Byrd admitted it could easily have gone the other way.

"I took this man lightly," said the 33-year-old American. "I came here thinking I'm the man, thinking about Lennox Lewis. He could easily have won this fight."

It was Oquendo's second professional defeat in a career that includes 24 victories.

Byrd began well but Oquendo fought back with some fierce counter-punching to knock the champion off his stride.

The Puerto Rican continued to trouble his opponent with some strong jabs although Byrd managed to up the tempo more in the closing rounds.

Byrd fell to the canvas in the 12th round after an effective combination from Oquendo, but the referee ruled it was not a knockdown.

On the undercard, Alejandro Garcia stopped the previously unbeaten Rhoshii Wells in the 10th round to retain his WBA super-welterweight title.