Dronfield's Lewis Taylor suffered heartbreak at Bramall Lane tonight.
An accidental head clash with Jamie Cox led to the fight being stopped in round nine.
It went to the judge's scorecard and Cox deservedly got the nod - winning the vacant WBA Continental super middleweight title.
Both fighters let their hands go in the first round, Cox eager to please his new Matchroom employers.
Heads clashed early on though and Taylor suffered a cut on the top of his forehead.
The Derbyshire man, 27, had success moving to his left and countering the aggressive Cox, who was a Brook sparring partner before the world title Errol Spence fight tonight.
Taylor had to take some punishment and fared better when he stepped around the incoming man and threw out long shots from range.
The home fighter has quick feet for a big man and was organised well behind a high guard.
In round five Taylor had to absorb a few nasty combinations on the ropes - Cox being warned later to keep his punches above the belt.
A nasty cut was opening up above Taylor's eye though, possibly through another head clash.
The Keith Palmer-trained local lad was finding his range every so often and started to dictate the tempo.
But blood was flowing into his eye and a doctor's advice in round nine was to call it a day.
Cox said Taylor had boxed the right fight, and he himself had been over-eager.
He predicted Brook would win.