Referee Howard Foster stopped the fight in the sixth of 12 scheduled rounds at London's Copper Box Arena after the ringside doctor had twice inspected Joyce's puffed up right eye, which was almost closed.

"Today belongs to me...I’m 39 years old, but I’m disciplined, I train hard. Next step I'm going for the title," Zhang said through a translator after punching the air and shouting 'Chinese Power'.

Two of the three judges had Zhang ahead at that point.

Joyce was the WBO 'interim' champion in the division -- a title that effectively made him the WBO's mandatory challenger for WBO, IBO, IBF and WBA champion Usyk. Britain's Tyson Fury holds the WBC title.

Zhang and Joyce are both Olympic silver medallists, the Chinese as a super-heavyweight at home in Beijing in 2008 and the Briton in the same division in Rio de Janeiro in 2016.

The Chinese had his shorter and lighter opponent in trouble from early on, Joyce providing a static target for Zhang's booming left hand and providing plenty of work for his corner as cuts opened up.

"I'm just disappointed with my performance," Joyce told BT Sport after what was his 16th pro fight. "The right hand he kept hitting me with. I couldn't get out of the way, so respect to Zhilei Zhang, Big Bang.

"I haven't fought a southpaw for so long...I expected to win like I normally do.

"I'll be back. My journey's not over, this is just a hurdle I may have tripped over so I'll be back."