By Mike Collett-White
LONDON (Reuters) - China's Liu Xiang left the Olympic stadium in a wheelchair on Tuesday after hitting the first barrier in a 110 metre hurdles heat while Jamaican Usain Bolt breezed through an "easy" 200 qualifier in his favourite event.
The contrasting fates of two of the world's most famous athletes made for a striking opening to the 11th full day of competition in London, where Britain celebrated more golds to make it the hosts' most successful Olympics in 104 years.
Later on Tuesday, Kenya's world and Olympic champion Asbel Kiprop will defend his 1,500 title while Australian women's 100 hurdles world champion Sally Pearson is favourite to improve on the silver she took in Beijing at 2000 GMT.
Liu's dreams of glory, however, were shattered in a cruel echo of his early exit from Beijing four years ago, and indications were that it was the same Achilles injury that led to his fall on a cool, cloudy morning in London.
China's first male gold medallist on the Olympic track after triumphing in 2004, Liu remains his country's most popular sportsman alongside former basketball player Yao Ming.
Fans at home quickly took to social networking websites to voice their dismay.
"My heart is broken," wrote one on Chinese microblogging service Sina Weibo. "I had been awaiting this race with such expectation."
Fellow athletes expressed their sympathy for Liu.
"It is really hard for him because I think he is one of the best hands down," Bolt told reporters.
"He has shown the world he can do great things. For him to push himself and come back last year ... for this to happen, this is really sad for any athlete."
Bolt, who set the second fastest time ever in his weekend 100 metres triumph, brimmed with confidence after qualifying comfortably for the 200 semis before another capacity 80,000 crowd at the main stadium.
He remains on course for an unprecedented Olympic sprint "double-double" at Thursday's final, although he may have to do it without the skipping rope he uses to train.
On his way into Sunday's 100 final an official removed the rope, saying it was against the rules, and Games chief Sebastian Coe has ordered an investigation into why it was confiscated.
Bolt, who has described some of the rules at the Games as "weird", said he planned to bring the rope with him on Thursday.
"I am going to do it tomorrow ... I am going to stick it under my bag, bottom of my bag or something."
Kenya's Kiprop, the world's fastest man over 1,500 this year, will have one thing on his mind in London - to win properly.
The world champion has often expressed his dissatisfaction at taking Olympic gold in Beijing after Bahrain's Rashid Ramzi was stripped of the title for a doping offence.
Hurdler Pearson, who has run the event's fastest time since 1992 of 12.28 seconds, will face competition from American duo Lolo Jones, who stumbled in the final while favourite in Beijing, and defending Olympic champion Dawn Harper.
Home nation Britain surpassed the heroics of four years ago, when they picked up 19 golds, by amassing 22 and counting.
Triathlete Alistair Brownlee crossed the line in central London's Hyde Park draped in the Union flag to make it 19, with his younger brother Jonathan taking bronze. Britain's horse riders triumphed in the dressage arena at Greenwich Park.
At the velodrome, where the crowd's roars were deafening, Chris Hoy won his seventh Olympic medal, and sixth gold, with victory in the keirin, taking him past rowing great Steve Redgrave's five golds.
He also matched fellow cyclist Bradley Wiggins as Britain's most decorated Olympian, although Wiggins has only four golds.
Laura Trott won in the cycling track omnium, but Victoria Pendleton, favourite to prevail in the individual sprint, lost out to Australian arch rival Anna Meares.
For Pendleton, who retires after the Games, it was a disappointing end to a glittering career that has delivered two Games golds and nine world titles.
Tuesday strengthened Britain's third place in the overall medals table in London, success which has helped fuel huge Games excitement across the country a year after London and other cities were.
By 1750 GMT on Tuesday, China led the overall medals table with 34 golds after picking up two in the gymnastics. Deng Linlin beat her compatriot Siu Lu to the balance beam title an hour after Feng Zhe had won the parallel bars title.
Flying Dutchman Epke Zonderland caused an upset, however, by claiming the horizontal bar title ahead of Chinese favourite Zou Kai who could only manage bronze.
The United States was second with 30 golds, including 16 in swimming.
Elsewhere on Tuesday, Dutchman Dorian van Rijsselberghe became the last ever men's RS:X windsurfing champion at the Olympics, with the event being replaced by kiteboarding in 2016 at the Rio de Janeiro Games.
Marina Alabau Neira of Spain won the women's title, while also on the water, but in a very different event, Italian kayaker Josefa Idem made the final aged 47.
The first woman to compete in eight Olympic Games is aiming to add to her gold from Sydney, two silvers from Beijing and Athens and bronzes from Atlanta and Los Angeles.
"I don't care about age," a smiling Idem told reporters after powering past a field of 20 and 30-year-olds in the semi-final. "The stopwatch doesn't ask."
Canada's women soccer players were less happy, accusing Norwegian referee Christiana Pedersen of bias towards the United States after their dramatic 4-3 extra-time defeat in the tournament semi-final on Monday.
Pedersen took the rare step of penalising Canadian goalkeeper Erin McLeod for holding the ball too long.
"We feel like we got robbed in this game," McLeod said.
Late on Monday, Cameroon's ministry of sports and physical education said seven athletes had disappeared while in Britain for the Olympics.
The five boxers, a swimmer and a soccer player may have vanished to seek a more prosperous life in Europe, but the International Olympic Committee said on Tuesday it was not aware of the incident.
(Additional reporting by the Reuters Olympic team; Editing by Mark Meadows and Mark Trevelyan)