South African "blade runner" Oscar Pistorius made history as the first double amputee to compete at the Olympics on an action-packed "Super Saturday" in London, where the world's fastest man Usain Bolt also opens the defense of his 100 meters title.

A capacity crowd of 80,000 in the main stadium roared as Pistorius, one of sport's most inspiring and controversial stories, qualified for the 400 meters semi final, and excitement built ahead of the first appearance of the fastest men on Earth.

In the pool, Michael Phelps has one last chance in the pool to add to the biggest Olympic medal haul of all time, while 25 medals in events ranging from tennis at Wimbledon to rowing in Windsor will be decided.

But the main drama was in the athletics arena, where Jamaican Bolt aims to secure a berth in Sunday's short dash final and repeat the heroics of Beijing where he won three golds and lit up the world with his lightning bolt celebrations.

Also limbering up for Sunday's final, the most prestigious event of the Games, will be the three other fastest men in history, all intent on toppling him: fellow Jamaicans Yohan Blake and Asafa Powell, and Tyson Gay of the United States.

Pistorius raised his arm aloft to acknowledge his warm reception. Born without a fibula in both legs, he had to fight for the right to line up against able-bodied competition, racing in his carbon fiber prosthetic blades.

"I was so nervous this morning," an elated Pistorius told reporters after the race. "Thanks to everyone for showing their support. I didn't know whether to cry."

Later on Saturday the women sprinters do battle in the 100m final with American Carmelita Jeter favorite, but defending champion Shelly-Ann Fraser and her fellow Jamaican Veronica Campbell-Brown will be out to keep the title in the Caribbean.

The last night of swimming action will see Phelps join his American team mates in the 4x100 meters medley final and looking for his 22nd Olympic medal.

Phelps, who this week smashed the previous record of 18 that Soviet gymnast Larisa Latynina had held for nearly half a century, notched up number 21 on Friday with gold in the 100 meters butterfly.

"This is my last individual event. It was awesome," Phelps said. "This swim was pretty important to me. I wanted to win."

Katie Ledecky, 15, took the women's 800m freestyle title, but the win was soured by questions over whether she had taken performance-enhancing drugs to destroy the field including home hope Rebecca Adlington.

Ledecky described as "totally false" suggestions she doped, in an unsavory echo of earlier in the Games when doubts were raised over the performance of China's 16-year-old swimming sensation Ye Shiwen, who notched two golds and a world record.

Another teenage U.S. swimmer, 17-year-old Missy Franklin, grabbed her third gold medal of the Games in the 200m backstroke, breaking the world record in the process.

"It hurt so bad in the last 25, that's the part that I love, knowing that I'm pushing myself past the limit," Franklin said.

She too will be looking for a medley relay gold to set the seal on her first Olympics.

Their feats propelled the United States to the top of the overall medals table for the first time, leading China by 21 golds to 20.

FIERCE KICK

On Friday's first day of athletics action in the Olympic Stadium, Ethiopia's Tirunesh Dibaba grabbed gold in the women's 10,000 meters by kicking fiercely at the bell to shake off two Kenyan rivals.

Dibaba, the defending champion, strode out to beat Sally Kipyego by some 30 meters, with world champion Vivian Cheruiyot taking the bronze.

Poland's Tomasz Majewski became the first man for 56 years to win back-to-back Olympic shot put titles by hurling 21.89 meters to beat world champion David Storl of Germany by three centimeters.

With cameras flashing, music blaring and 80,000 fans creating a deafening roar, British favorite Jessica Ennis captured the lead in a see-saw heptathlon contest.

Ennis, Britain's Olympic poster girl, set a world best time in the 100 meters hurdles and followed with a solid high jump, but was pegged back by Lithuania's Austra Skujyte who bettered her by more than three meters in the shot put.

She took a lead of 184 points into the second day of the event, which concludes with the long jump, javelin and 800m.

Among the other track medals to be decided was the women's 100m final in which world champion Jeter ran the fastest time in the heats, sprinting home in 10.83 seconds.

FEDERER EPIC

In the first medal of a hectic day, Switzerland's Nicola Spirig won the women's triathlon in a photo finish at the line with Lisa Norden of Sweden.

Britain's rowers edged out their fierce rivals Australia in the men's four event, the most eagerly-anticipated of the races at Dorney Lake in Windsor, near London.

The victory before 30,000 screaming fans gave Britain its fourth consecutive win in the discipline and took the host nation's medal tally on the course to seven medals, making it the most successful Olympic rowing regatta for the country in the modern era.

Britain was already celebrating on Friday, when Katherine Grainger and Anna Watkins won the in double sculls rowing - a dream come true for Grainger after three previous silvers.

In track cycling, there were also golds for the host nation's men's team pursuit cyclists and Victoria Pendleton in the women's keirin.

Britain demolished Australia and their own world record to defend the men's Olympic team pursuit gold medal they won four years ago in Beijing and send the home crowd into a state of delirium once again in the velodrome on Friday.

David Bowie's "Heroes" blasted out over the tannoy as the home fans clapped the gold medalists on a lap of honor after they shaved almost a second off the previous record.

The victories have put Britain in third place in the medals table with nine golds, just ahead of South Korea.

At Wimbledon, Roger Federer of Switzerland remained on course to repeat his heroics in the grasscourt grand slam in July, beating Argentina's Juan Martin del Potro in a marathon 19-17 third and final set to earn a place in the final.

Federer will now face local hope Andy Murray, who rode a wave of British euphoria to beat Serbia's world number two Novak Djokovic 7-5 7-5 and set up a repeat of last month's Wimbledon final against the Swiss maestro.

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