LONDON (Reuters) - Usain Bolt answers the nagging question of whether he is still the fastest man on Earth on Sunday in an Olympic cauldron that almost boiled over when Britain's athletes enjoyed their greatest night on Saturday.

Jamaica's Usain Bolt finishes first in his men's 100m round 1 heats at the London 2012 Olympic Games at the Olympic Stadium August 4, 2012. REUTERS/Dylan Martinez

The Jamaican won a golden treble with three astonishing world records at the last Olympics in Beijing. But since then he has lost his world title and his aura of invincibility.

Fans hoping the men's 100 metres final (2055 GMT) on the fast London track will top Beijing's may not have been reassured by the sight of Bolt stumbling as he qualified for Sunday's semi-final (1845 GMT). Still, few would against him bet against him stepping up a gear or several.

The final is also expected to include the three fastest men in history after Bolt - Jamaica's world champion Yohan Blake, compatriot Asafa Powell and Tyson Gay of the United States - meaning Jamaica could scoop the 1-2-3 in London on the eve of the 50th anniversary of its independence from Britain.

Asked by reporters if he was in good enough shape to follow compatriot Shelly-Ann Fraser-Pryce and win back-to-back Olympic 100 titles, Bolt looked down at his feet and replied: "We'll see."

If Sunday could rewrite the record books, Saturday belonged to hosts Britain, who took three athletics golds in less than an hour, plus two in rowing and one in the velodrome to register their best day at an Olympics since the first London Games in 1908.

Games chief Sebastian Coe described it as "the greatest day in sport I have ever witnessed". No mean praise from a double gold medallist whose own Olympic middle-distance duels with Steve Ovett in the 1980s framed the sporting memories of a generation of Britons.

GOLD RUN

"Their extraordinary efforts have brought rapture to streets, parks and living rooms in London and all over the country if not the planet," Mayor of London Boris Johnson said, summing up a euphoric mood after Britain's gold rush.

The home gold run continued on Sunday when Ben Ainslie became the most successful Olympic sailor of all time, winning the Finn class gold in the waters off Weymouth on England's south coast to make it one silver and four straight golds.

British defending champions Iain Percy and Andrew Simpson had to settle for silver in the Star class after Sweden's Fredrik Loof and Max Salminen sailed a perfect medal race for gold.

In an exhilarating hour on Saturday night, Jessica Ennis, British poster girl of these Olympics, collapsed in tears of relief after a capacity 80,000 crowd roared her to victory in the heptathlon.

She confirmed on Sunday that she would not run in the individual 100 hurdles later this week as she looks forward to some rest - as well as vast British media attention and a slew of sponsorship opportunities that will inevitably follow.

Greg Rutherford was also hailed a hero by British newspapers after winning a surprise long jump gold while Mo Farah, born in Somalia but brought up in England, took Britain's first 10,000 gold to break 16 years of Ethiopian domination in the event.

"I just can't believe it, the crowd got behind me so much. I've never experienced anything like this. The best moment of my life," Farah said.

Former Beatle Paul McCartney led the crowd on Saturday in singing "Hey Jude" to serenade the women's team pursuit cyclists who made it four golds for Britain in five track cycling events.

The customary "Dorney Roar" also pushed two British rowing crews to gold and one to silver on Lake Dorney outside London.

SERENA SOARS

Andy Murray was shouldering Britain's dreams at Wimbledon on Sunday, aiming to avenge his defeat by Swiss world number one Roger Federer in last month's grand slam final. Murray is also due to team up with Laura Robson for the mixed doubles final.

Serena Williams took her second tennis gold of the Games, retaining the women's doubles crown for the United States with her sister Venus after her 6-1 6-0 rout of Maria Sharapova in the women's singles final on Saturday.

But she has a way to go to emulate the most decorated Olympian of all, her countryman Michael Phelps, who was given a rapturous send-off in the pool on Saturday at the end of his competitive career.

Phelps swam his favourite butterfly stroke in his farewell race to help the United States to victory in the 4x100 medley relay, an event they have never lost.

The medal was his 18th gold in an Olympic career stretching back to Sydney in 2000 and his 22nd of any colour, four more than the previous record held by Soviet gymnast Larisa Latynina.

"I've been able to do everything I wanted," he said. "I've been able to put my mind to the goals that I wanted to achieve and (coach) Bob (Bowman) and I have somehow managed to do every single thing."

Sporting history was made in the boxing ring on Sunday when Russia's Elena Savelyeva won the first women's Olympic boxing bout, bringing an end to the last all-male preserve at the Games in front of a packed crowd.

Rejected in the past because of a perceived lack of global interest, women boxers were give a warm welcome in London when Savelyeva and North Korea's Kim Hye-song were enthusiastically clapped into the ring for the first of Sunday's 12 fights.

The first gold of the 23 up for grabs on Day Nine was taken by Tiki Gelana of Ethiopia, who won a women's marathon that started and finished in torrential rain on a course that took in many of London's big tourist attractions.

South Korean Jin Jong-oh produced a stunning display to overturn a huge deficit against compatriot Choi Young-rae and retain the men's 50 metre pistol title on Sunday for his second gold of the Games.

China took two golds, with Lin Dan winning the men's badminton singles and Zou Kai topping the podium in the men's gymnastics floor final - leaving China and the United States neck and neck in the medals table with 27 golds apiece, ahead of Britain in third.

(Editing by Kevin Liffey)

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