Wilder, 38, was defeated by Joseph Parker in December and insisted he would hang up the gloves if he were to lose to 41-year-old Zhang.
After a tentative opener, Zhang began to walk Wilder down with the Alabama fighter throwing little back.
Wilder sprang into action in the fifth after being told by his corner to show more explosiveness, but seconds later he turned his back after Zhang landed a solid right hand.
As Wilder turned back towards his opponent, he was met with a more brutal right.
The sorry sight of the ‘Bronze Bomber’ – who left the ring without giving any post-fight interview – sprawled across the ring and using the rope to aid him back to his feet may just be the last time boxing fans see him in the ring.
Warren meanwhile ended the night with a beaming smile having got the better of Hearn in a family rivalry that dates back to the 1980s.
Matchroom and Queensberry had been at odds ever since Hearn’s father, Barry, began promoting boxing events in that decade.
From the very first fight onwards, Hearn and Warren bellowed instructions and encouragement from ringside. Hearn would jump out of his seat and Warren was seen banging the canvas.
The feud was repaired last year when energy-rich Saudi Arabian organisers convinced Hearn and Warren to bury the hatchet and work together, and there are already plans for more team events to take place in the near future.
“This is a formula for the future and we want to continue doing this,” Warren said as he shared a handshake with Hearn and took home the £2.3m ($3m) bonus .