Charlie Edwards retained his WBC flyweight title as his bout against Julio Cesar Martinez was ruled a no-contest - moments after the mandatory challenger had been declared a winner.
The Londoner's nine-month reign as world champion seemed to be over when he was counted out after a relentless assault to the body from the Mexican in the third round.
However, the final punch to the ribs came after Edwards had taken a knee and once the incident had been shown on the big screens at the O2 Arena, a knockout victory for Martinez was overturned because of the illegal blow.
WBC president Mauricio Sulaiman told Sky Sports: "This fight has been ruled a no-contest and a direct rematch will be ordered."
Edwards was making the second defence of his title against an opponent who earned his opportunity following a fifth-round knockout of Andrew Selby in Mexico in March.
Boos rang out around the O2 Arena following the controversial ending but they turned to cheers following Sulaiman's announcement.
Edwards said: "He did hurt me, I won't deny that, and that's why I took a knee. But it was the shot on the floor that put me away.
"I took a knee for a purpose. He finished me off with a body shot. Cheaters never prosper."
