Enzo Maccarinelli took just over a minute to make the first defence of his WBU cruiserweight title.
Enzo Maccarinelli's uppercut did all the damage
The Swansea fighter sent opponent Andrei Kiarsten crashing to the canvas with a stunning right uppercut in the first round at the Newport Centre.
Maccarinelli, who only found out he was fighting the Russian last week, said: "Kiarsten was a dangerman who could box.
"He was strong and had been in with a lot of tough Eastern Europeans, but I hit so hard that as soon as I connect I know I'm going to take them out."
Promoter Frank Warren says the 23-year-old will make a quick return into the ring as he continues his development as a professional fighter.
"He'll fight again before Christmas," Warren told BBC Sport. "We want to keep him busy.
"But it's a Catch-22 situation - we obviosuly want him to finish fights quickly, but the longest he's ever been is four rounds.
"It's important from his point of view that we get someone who is going to help him get some rounds under his belt."
On the undercard, WBU light-middleweight champ Takaloo retained his title with a comfortable win over Wladmir Borovski in three rounds.
Newport Sports Centre card, 13 September
Enzo Maccarinelli bt Andrei Kiarsten (KO 1)
WBU cruiserweight title
Takaloo bt Wladimir Borovski (KO 3)
Michael Monaghan bt Thomas Da Silva (points 60-54)
Jamie Arthur bt Jez Virdee (KO 1)
Tony Doherty bt Darren Colvill (points 40-36)
Scott Gammer bt Derek McCafferty (points 60-54)