Terri Harper lost her world title to Alycia Baumgardner as the Brit appeared to be knocked out while still standing.
Harper was returning to the ring for the first time in a year having broken her hand in her previous performance.
And she looked off the pace from the opening bell, surviving a scare in the second round before being stopped minutes later.
Baumgardner landed a right hand which staggered Harper who then appeared to be knocked out while remaining standing.
The new champion was able to land a follow-up left hand but referee Mark Lyson stepped in quickly to stop the fight.
And analyst and former world champion Tony Bellew later said Harper had been "asleep on her feet".
Baumgardner, who had lost one of her 11 professional fights, said: "Ive dreamed of this moment, I put it in my head and looked at myself in the mirror every day and told myself I'd be world champion.
"Coming here I saw her energy. When I came over here as the challenger, my confidence was 100 and I didn't see that in her.
"I know a lot of people haven't seen me but I was given a platform to show that I can box and fight."
Harper won her world title when she beat Eva Wahlstrom early last year before fighting to a draw with fellow Brit Natasha Jonas.
She stopped Katharina Thanderz 12 months ago to retain her title but was forced to have a second operation on her hand.
Baumgardner had the advantage of having fought in August but she faced a considerable step up against Harper.
But she was on the front foot from the opening seconds as she seized her opportunity against the ring-rusty champion.
Harper offered to argument about the stoppage and left the ring quickly after the result was officially announced.
Promoter Eddie Hearn confirmed Harper has the option of a rematch but acknowledged his fighter has suffered a brutal defeat.
Earlier, Chris Billam-Smith retained his European cruiserweight title by labouring to a points win over Dylan Bregeon.
