Paul Butler failed in his bid to become a two-weight world champion, suffering a first career defeat by South Africa's Zolani Tete in Liverpool.
Tete stopped his opponent in the eighth round of the IBF super-flyweight title fight after landing with an uppercut.
"I knew Paul was a good fighter, but I knew I could knock him out," 26-year-old Tete told BoxNation.
Butler, also 26, dropped a division for Friday's contest at the Echo Arena but lost his 18th professional fight.
"I normally have people come towards me. He's a very big kid, and we knew his power by his record. He's a great champion," Butler said.
The South African southpaw, who has held the title since July, now has a fight record of 20-3 with 17 knockouts.
Chester-born Butler won the IBF bantamweight title from British rival Stuart Hall last year but relinquished it immediately.
Meanwhile, Liverpool lightweight Derry Mathews (37-9-2) secured a fifth-round knockout against Hungarian Gyorgy Mizsei Jr.
"Mizsei Jr has been in with some of the best fighters in Britain but I don't think any of them have done what I did. I hit him with the perfect shot and he never recovered," the 31-year-old said.
Mathews next faces a fight against Richar Abril for the WBA world title at the Echo Arena on 18 April.