By Kevin Liffey
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.
The Jamaican claimed 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 meters final on the fast London track will top Beijing's may not have been reassured by the sight of Bolt shorn of his trademark cockiness after stumbling in his heat and qualifying ninth fastest.
The semi-finalists earlier in the day will be led by American Ryan Bailey, who clocked 9.88 seconds in the heats, and Justin Gatlin (9.97).
But the semis also include the three fastest men in history after Bolt - Jamaica's Yohan Blake and Asafa Powell and Tyson Gay of the United States.
Bolt has suffered fitness niggles and said as the Games began that he was "95 percent" fit.
Asked by reporters on Saturday if he was in good enough shape to win gold, Bolt looked down at his feet and replied: "We'll see".
He can at least take inspiration from a crowd who cheered his first appearance to the hilt and from compatriot Shelly-Ann Fraser-Pryce who on Saturday repeated her own Beijing victory in the women's 100.
She clocked an impressive 10.88 seconds to hold off American Carmelita Jeter and give Jamaica a chance of repeating their Beijing sweep of individual 100 and 200 golds.
But Saturday night belonged to Britain who took three athletics golds and three more elsewhere to register their best day at an Olympics since the first London Games in 1908.
Jessica Ennis, poster girl of these Olympics, collapsed in tears of relief after a capacity 80,000 crowd roared her to victory in the heptathlon.
Greg Rutherford then won a surprise long jump gold and finally Mo Farah, born in Somalia but brought up in England, won Britain's first 10,000 meters gold to break 16 years of Ethiopian domination in the event.
Kenenisa Bekele, winner at the last two Olympics, finished fourth.
"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.
British medal success and the exuberance of fans across the venues have begun to create an Olympic buzz across Britain.
On Saturday former Beatle Paul McCartney got in on the act by leading the crowd in singing the 'Hey Jude' hit 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.
Britain have made little impact in the pool but that did not stop the crowd giving a rapturous send-off to the most decorated Olympian of all.
Michael Phelps swam his favorite 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 color, 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."
One American as hungry for glory as ever is Serena Williams.
Her 6-1 6-0 rout of Maria Sharapova in the final on Wimbledon's Centre Court sealed a 'Golden Slam' of all four major tennis titles plus Olympic singles gold.
She has also won two Games doubles titles with sister Venus and the duo are favorites to add another on Sunday when they play Czechs Andrea Hlavackova and Lucie Hradecka.
The tennis also gives the host nation a chance of more gold on Sunday when Andy Murray tries to ride Britain's Olympic wave to avenge his Wimbledon defeat to Roger Federer on the same court exactly four weeks ago.
The Swiss is the favorite but Murray has a second shot at gold later as he partners Laura Robson against Belarus pair Victoria Azarenka and Max Mirnyi in the mixed doubles final.
The men's doubles title went to the American twins Bob and Mike Bryan who also secured a doubles 'Golden Slam' with a 6-4 7-6 win over France's Jo-Wilfried Tsonga and Michael Llodra.
United States finished Day Eight at the top of the medals table with 26 golds followed by China on 25 and Britain on 14.
The Americans cemented their dominance in the pool by winning the women's medley relay in world record time but had to share the last-night swimming limelight with China's Sun Yang.
Sun slashed more than three seconds off his own world record to win the men's 1,500 freestyle to go with his 400 gold.
Dutchwoman Ranomi Kromowidjojo won the 50 freestyle. Having already claimed the 100, she is unchallenged as the fastest woman in the pool.
In London's Hyde Park, the women's triathlon came down to a photo-finish, the first in the sport.
After just shy of two hours of swimming, cycling and running, Switzerland's Nicola Spirig was judged to have beaten Lisa Norden of Sweden by just 15cm (six inches) in a ferocious sprint finish that Sunday's 100 meters cast will do well to match.
(Additional reporting by Karolos Grohmann, Mitch Phillips, Steven Downes and Kate Holton; editing by Tony Jimenez)
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