Xiao triumphed in the pommel horse event, while Greece's Eleftherios Petrounias maintained his dominance of the rings discipline with a third straight gold medal and Russian Artur Dalaloyan added the floor title to his individual all-around triumph.

Biles earned her third crown in Doha as she topped the vault podium having scored an average of 15.366 over her two attempts at the Aspire Dome in Qatar's capital.

The 21-year-old has now broken the all-time record for gold medals at the World Championships set by Belarusian male gymnast Vitaly Scherbo in 1996.

Canada's Shallon Olsen took silver with a score of 14.516, while bronze went to Mexico's Alexa Moreno.

Biles was denied a second gold medal as she finished behind Belgium's Nina Derwael, the first female Belgian gymnast to win a world title, in the uneven bars.

It would have been a surprise to see the American take gold on the apparatus, however, as she openly admits it is her weakest event.

Derwael scored a total of 15.200, 0.500 ahead of Biles, while Elisabeth Seitz of Germany took bronze on 14.600.

Biles had admitted her disappointment with her gold medal-winning performance in the individual all-around and admitted she was much happier today.

"I’ve come a long way (on the bars) and I’m really pleased with the performance I put out today,” she said.

“I really put the work and the effort in to bring that event up to the same standard as the others.

“I think I’m off to a good start and hopefully it gets the ball rolling for tomorrow.

“It (my kidney stone) feels pretty good but when I go home from this I’ll be going straight to the doctor the next day."

Ruoteng, who fell agonisingly short of defending his men's all-around title when he lost out to Russian Artur Dalaloyan on countback, edged Olympic and two-time defending champion Max Whitlock in a tense pommel horse.

The Chinese gymnast and Whitlock both ended on 15.166 points, with Xiao declared the victor by virtue of his higher execution score.

Lee Chih Kai of Chinese Taipei claimed bronze on 14.966.

Petrounias, the Olympic rings champion, had not been beaten at a major international competition since 2015 and demonstrated exactly why with another flawless performance.

The 27-year-old scored 15.366 to beat Brazil's Artur Zanetti, who took silver on 15.100, and bronze medallist Marco Lodadio of Italy.

Dalaloyan was again in superb form, scoring 14.900 to beat renowned twister Kenzo Shirai of Japan, whose difficulty was higher than the Russian.

Carlos Yulo of the Philippines took bronze.

The event concludes tomorrow with the last five apparatus finals.