United States' gold medallist Michael Phelps, front, walks with South Africa's silver medallist Chad le Clos behind him after the medal ceremony for the men's 100-meter butterfly swimming final at the Aquatics Centre in the Olympic Park during the 2012 Summer Olympics in London, Friday, Aug. 3, 2012. (AP Photo/Matt Slocum)

LONDON - "Bladerunner" Oscar Pistorius was cheered around the Olympic track Saturday, finishing second in his 400-meter heat to advance to the next round on his carbon fiber blades.

The South African double amputee circled the oval with 80,000 fans cheering him on in 45.44 seconds — good enough for second place in his heat and a berth in the semifinals Sunday night.

The 25-year-old Pistorius was born without fibulas and his legs were amputated below the knee before he was a year old.

In an early gold medal Saturday, Nicola Spirig of Switzerland outsprinted Sweden's Lisa Norden in the final meters to win the women's triathlon. Spirig crossed the line after the 10-kilometre run leg just a fraction ahead of Norden, with Erin Densham of Australia taking the bronze.

Later in the day at the Aquatics Centre, an era of unprecedented sporting domination comes to an end when Michael Phelps swims his last competitive race.

Phelps is heavily favoured to add one more gold to his collection of 21 Olympic medals, 17 of them gold, when he swims the butterfly leg of the 4x100 medley relay, a race the Americans have never lost.

The 27-year-old swam his first Olympics in Sydney 12 years ago and is retiring after London.

At the Olympic rowing site west of London, Britain maintained its dominance of the men's four by taking gold for a fourth consecutive games. The crew of Alex Gregory, Pete Reed, Tom James, Andrew Triggs Hodge crossed the line ahead of Australia and the United States.

The gold was Britain's seventh medal of the regatta to surpass its total from Beijing four years ago, making it the country's biggest rowing haul in the modern era.

At the All England Club, Maria Sharapova and Serena Williams will both be playing not only for a gold medal, but a so-called Golden Slam. Each is seeking a first Olympic title to add to their career majors.

Williams said she was more concerned with winning another medal for the American Olympic team, than with adding to her list of titles.

"Whether I win or lose, that's not the big deal," Williams said. "The big deal for me, USA is guaranteed another medal. I'm guaranteed to just go out there tomorrow and have fun. That's all I can do."

The Olympic women's doubles badminton tournament, marred by a match-throwing scandal this week, ends Saturday with the final between a Chinese and a Japanese pair.

Earlier this week, another Chinese pairing, along with two teams from South Korea and one from Indonesia, were thrown out of the competition for attempting to throw their games to secure a better more favourable draw in knockout play.

In the second day of athletics, local favourite Mo Farah runs in the 10,000 metres against stiff competition including Kenenisa Bekele of Ethiopia and another British medal candidate, Jessica Ennis, completes the heptathlon.

The women's 100-meter final will provide another indication of just how fast the track is in the 80,000-seat Olympic Stadium.

Led by world champion Carmelita Jeter's time of 10.83 seconds, seven sprinters — including defending champion Shelly-Ann Fraser-Pryce of Jamaica — ran the first round of the 100 in 11 seconds or better on Friday.

Usain Bolt also will begin the defence of his men's 100-meter crown in the first round of heats.

Outside the stadium and in the centre of London, the men's 20-kilometre walk ends with a not-very-leisurely stroll along The Mall, the broad, tree-lined avenue running between Buckingham Palace and Trafalgar Square.

Britain aims to continue its dominance on the Siberian pine boards at the Velodrome with the women's team pursuit.

News from © The Associated Press, 2012