Marco Antonio Barrera suffered only his fourth defeat in 62 fights when he was stopped by Manny Pacquiao in San Antonio on Saturday.
Barrera had to seek permission to take the bout
Mexican great Barrera saw his challenge end when his corner threw in the towel in the closing seconds of round 11.
Pacquiao, of the Philippines, touched down in the opening round but recovered to floor his opponent twice.
Barrera, who deprived British boxer Naseem Hamed of his unbeaten record in 2001, picked up a cut in round seven.
And he was then deducted a point for an intentional headbutt in the ninth as the fight slipped away, with the pressure becoming too much in the 11th.
There was some concern for Barrera before the fight when he revealed that he would be fighting with a metal plate in his head.
Barrera has suffered with headaches since 1995 undergoing minor brain surgery in 1997, and had to seek permission to take the bout by Texas authorities.
"Tonight just wasn't my night," said 29-year-old Barrera. "There were a lot of distractions, examinations and breaking up of the camp.
"I couldn't see a lot of things, I wasn't really concentrating and I wasn't feeling myself. I feel real disappointed."
IBF junior featherweight champion Pacquiao said: "I'm surprised he lasted that long."