* Fraser-Pryce extends Jamaican sprint dominance
* Britons win heptathlon, men's long jump and 10,000 metres
* Phelps finishes with 18th gold, record 22nd Olympic medal
* Serena Williams wins women's tennis title
* "Blade runner" Pistorius makes Games history (Updates with women's 100 metres and men's 10,000)
By Kevin Liffey
LONDON, Aug 4 (Reuters) - Three athletics golds crowned host nation Britain's best Olympic day for over a century after the greatest swimmer of all time bowed out on a high by winning Saturday's last pool race of the Games.
Jessica Ennis, poster girl of the London Games, collapsed in tears of relief after a capacity 80,000 crowd roared her around the athletics track to victory in the heptathlon. More golds followed for Britain in the men's long jump and 10,000 metres.
On the day Jamaica's 100 metres world record holder Usain Bolt began his title defence, compatriot Shelly-Ann Fraser-Pryce won the right to call herself the fastest woman in the world by winning her second successive women's 100m Olympic gold.
American Serena Williams made short work of Maria Sharapova in the women's tennis final to seal a career "Golden Slam" of all four Grand Slam titles plus Olympic singles gold.
Day Eight of the Games had been billed as "Super Saturday", but the host nation's enthusiastic crowds could hardly have imagined that Britain would take six of the 25 golds on offer.
They had not won so many on a single day since the first London Olympics, in 1908.
In rowing, Britain finished as leading nation, winning two golds on the last day of competition, including the prized men's four. In the velodrome, where they have dominated, the hosts won the women's team pursuit to make it four golds out of five so far.
Britain finished the day third in the medals table on 14 golds, behind the United States on 26 and China on 25.
"I just had to give it everything at the end," Ennis said after winning the final 800m discipline. "I just wanted to make sure I gave them something and brought it all home."
Although Britain have made little impact at the pool that did not stop the crowd also giving a rapturous send-off to the most decorated Olympian of all.
Michael Phelps swam his favourite butterfly stroke in his farewell race to help the United States to victory in the 4x100m 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.
But the night in the stadium belonged to Britain.
First Ennis left the heptathlon field trailing, having recorded personal bests in three of her seven disciplines. Then Greg Rutherford won an unexpected long jump gold.
Finally, Mo Farah, born in Somalia but brought up in England, won Britain's first ever 10,000m gold, breaking 16 years of Ethiopian domination of 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.
The last word of the night belonged to Jamaica, where Fraser-Pryce just held off Carmelita Jeter of the United States to retain her Olympic 100m title in an impressive 10.75 seconds.
Her win could be the first leg of a Jamaican double with Bolt and Yohan Blake vying for the men's 100 gold on Sunday.
Bolt, the biggest draw of the Games, soaked up the applause of the crowd before comfortably winning his morning heat, albeit with a stuttering start.
"I made a bad step," the 25-year-old said. "I stumbled a bit. I'm glad it happened now."
Earlier in the day, South African "blade runner" Oscar Pistorius had made history of a different kind as the first double amputee to compete in an Olympic athletics event, coming through his 400 metres heat.
Pistorius raised his arm to acknowledge the cheers of the crowd. Born without a fibula in both legs, he fought for the right to line up against able-bodied competition, racing in his carbon-fibre prosthetic blades.
"I was so nervous this morning," an elated Pistorius told reporters. "Thanks to everyone for showing their support. I didn't know whether to cry."
But where there were thrills there were also spills as American defending men's 400m champion LaShawn Merritt, the fastest in the world this year, pulled up injured in his heat.
Former world 100m champion Kim Collins failed to appear for qualifying, vowing never to run for St Kitts & Nevis again after falling out with his country's Olympics officials.
On Wimbledon's Centre Court, Williams was in imperious form, thrashing Maria Sharapova of Russia 6-0 6-1 in just 62 minutes.
It made her the fourth player to win a career "golden slam" after Steffi Graf, Andre Agassi and Rafael Nadal.
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 limelight with China's Sun Yang.
Sun slashed more than three seconds off his own world record to win the men's 1500m freestyle to go with his 400m gold.
Ranomi Kromowidjojo of the Netherlands won the women's 50m freestyle. Having already won the 100m, she is unchallenged as the fastest woman in the pool.
In the velodrome, Britain's women's pursuit team took gold, breaking the world record for the third time in three races.
In London's Hyde Park, the women's triathlon came down to a photo-finish, the first ever 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 15 cm (6 inches) after a ferocious sprint finish.
Away from the sporting action, Colombian 400m runner Diego Palomeque Echevarria was suspended from the Games after testing positive for testosterone, the fourth athlete suspended by the International Olympic Committee (IOC).
Brazilian rower Kissya Cataldo da Costa has been sent home by her own federation for failing a pre-Games dope test.
"Cheats are being caught and ejected," said IOC spokesman Mark Adams. "At this stage it is a pretty low number."
Ironically, the bans came on a big day for prominent doping offenders Justin Gatlin and Dwain Chambers, who were selected to run in the 100m in London after serving long bans.
"I would clearly rather have that these competitors are not here," London Games chief Sebastian Coe told Reuters.
"The federation says they are eligible to compete, the IOC says they are eligible to compete so we give them as much courtesy as all the other athletes. The answer is that that is the world we live in." (Additional reporting by Karolos Grohmann, Mitch Phillips, Steven Downes and Kate Holton)