Filip Hrgovic has said he is still "angry" with himself at being outboxed by Moses Itauma despite beating him, and said the 21-year-old might never lose again.
Hrgovic (21-1, 16 KOs) stunned Itauma (14-1, 12 KOs) in August, stopping the Brit -- who was the heavy pre-fight favourite -- in Round 9 to win the IBF heavyweight title.
Despite Hrgovic's sensational win, the early signs pointed to victory for Itauma, who boxed well and landed big shots, with the Croatian touching the canvas in Round 2.
But, Hrgovic revealed after the fight he knew if he could withstand the early onslaught, Itauma would tire in the later rounds, saying the Brit boxed "like an amateur."
His moment came in Round 9 when Itauma became exhausted, forcing referee Howard Foster to stop the contest just as Itauma's trainer, Ben Davison, threw the towel in.
Reflecting on the fight, Hrgovic said he was annoyed at his performance in the early rounds.
"I'm still kind of angry. I'm happy, of course. I'm proud of myself, but I'm kind of angry because he outboxed me in first rounds," Hrgovic told media on Wednesday.
"I didn't expect that's going to happen because all my career, 20 years in boxing, I was never outboxed in any sparring, in any fight. Some rounds, you win, some rounds, you [lose], but I was always competitive ... And this kid outboxed me and he started very fast.
"I'm a little bit angry on myself that I allowed him to outbox me."
Itauma has vowed he would come back, is expected to return to the ring early next year.
Hrgovic said given Itauma's talent, he will go on to have a hugely successful career if he can learn from the experience.
"It was big shock for him, big humiliation, so maybe it's end of his career if he's not mentally tough," Hrgovic said.
"A lot of people after that kind of loss, they never come back. So, it will be a hard journey for him to come back. But, if he recovers and if he'll not lose his confidence, I think with this experience, what he gained from this fight, I think no one ever will beat him again.
"I think it's experience and it's not about physical preparation. And like I said, this will mean a lot for him, this kind of experience, and if he recovers and come back mentally strong, I think it's big experience and no one ever will beat him again."