China’s Liu Xiang left the Olympic stadium in a wheelchair on Tuesday after hitting the first barrier in a 110 metre hurdles heat, an unhappy echo of Beijing when his early exit due to injury was a bitter blow to the host nation.

The fall robbed the Games of one of its biggest draws on a day when Jamaican 100 sprint champion Usain Bolt returned to the track in a 200 qualifier and Britain equalled its Beijing gold medal tally of 19 with success in the men’s triathlon.

But at the main stadium, once again packed to the rafters with 80,000 roaring fans, the drama was dominated by 29-year-old Liu’s premature exit.

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.”

Liu is still plagued by the Achilles injury that forced him to pull out at the Bird’s Nest in Beijing four years ago but he had been in a rich vein of form this year.

Rival American hurdler Aries Merritt summed up the disappointment among fellow competitors.

“It was just terrible,” he told reporters. “That it happens to one of the best hurdlers of all time is just a tragedy.”

BOLT THROUGH

Bolt began his bid to complete an unprecedented Olympic sprint double-double when the Jamaican breezed through his opening 200 heat with the minimum of fuss on a cool, overcast day in London.

Less than 48 hours after retaining his 100 crown on Sunday, Bolt eased into Wednesday’s semi-finals of his favourite event by winning the opening heat in a pedestrian 20.39 seconds.

Bolt is hot favourite to follow up his Beijing 200 gold and wants to cement his place as a “legend” in the sport.

Later on Tuesday, 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.

Algeria’s Taoufik Makhloufi, who beat Kiprop in Sunday’s semi-final, was provisionally thrown out of the Games for not trying hard enough in an 800 heat on Monday but was later reinstated.

Makhloufi had not planned to compete in the heats but the International Association of Athletics Federations (IAAF) said his team had failed to withdraw him in time and he had to run.

When he stepped off the track, after jogging round for half a lap, the athletics referee disqualified him from all further events for not making a bona fide effort. H i s team said he had a knee injury and the IAAF eventually overturned the ban.

Women’s 100 hurdles world champion Sally Pearson is favourite to improve on the silver she took in Beijing at 2000 GMT.

The Australian, 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.

British hopes lay with the decorated trio of power cyclists Chris Hoy, Victoria Pendleton and Laura Trott, who are looking to cement the hosts’ dominance in the boisterous velodrome venue.

But it was at Hyde Park in central London that “Team GB” matched its impressive Beijing gold tally of 19 when Alistair Brownlee won the men’s triathlon. His brother Jonathan was third.

The victory rubberstamped Britain’s third place in the overall medals table in London. Their success has helped fuel huge Games excitement across the host nation.

By 1330 on Tuesday, China led the overall medals table with 31 golds, with the United States close behind on 29.

GRENADA FIRST

Monday saw a tearful Felix Sanchez of the Dominican Republic recapturing the Olympic 400 hurdles title at the ripe age of 34, eight years after he first won it.

“A lot of people said I should retire but I stuck with it,” said Sanchez. After finishing, he took out and kissed a picture of his grandmother Lillian, who died during the Beijing Games.

Youth won the day in the men’s 400, with Grenada’s 19-year-old world champion Kirani James dominating to take his nation’s first Olympic gold. Sanchez’s compatriot Luguelin Santos, also just 19, took silver.

“It is probably crazy at home right now, there is probably a huge party in the streets,” a jubilant James – nicknamed “The Jaguar” – told reporters.

Yelena Isinbayeva of Russia, bidding for a third successive gold medal in the women’s pole vault, could only manage bronze behind Jennifer Suhr of the United States, who went one better than her silver medal in Beijing, and Yarisley Silva of Cuba.

Russian world champion Yuliya Zaripova won the women’s 3,000 steeplechase, storming over the line well clear of Tunisia’s Habiba Ghribi and Ethiopia’s Sofia Assefa.