London, Aug 4 (IANS): American swimmer Michael Phelps won the men's 100-metre butterfly to take his Olympic golds to 17 and overall medals tally to 21, and thanks to a gold rush in the pool the United States overtook China at the top of the medals table.

Phelps clocked 51.21 seconds for the 100m title, adding to his victories earlier in the 200m individual medley and 4x200m freestyle relay Friday, reports Xinhua.

Chad le Clos of South Africa and Evgeny Korotyshkin of Russia touched in 51.44 to share the silver medal.

Until Thursday, no man had won an Olympic swimming title in three separate Games. Phelps ended that record with his win in the 200m medley and Friday's win means he has repeated the same feat in this race.

"I am just happy that the last one was a win. That is all I really wanted and this was by far a bigger winning margin than the last two combined," said the 27-year-old Phelps, who has announced he is retiring after the London Games.

Phelps will take part in his last race Sunday - the 4x100m medley relay.

Fellow American Missy Franklin also claimed her third gold medal of the games with a world record-breaking swim in the 200m backstroke.

The 17-year-old, who had already won the 100m backstroke and formed part of the US women's 4x100m freestyle relay, touched home in 2:04.06, eclipsing the previous best set by Kirsty Coventry in Rome in 2009.

With the women's 4x100m medley to be contested Saturday, Franklin has a chance to take her fourth gold, which will make her the most successful swimmer in London.

Fifteen-year-old Katie Ledecky, the youngest member of the US team, upset local favourite and defending champion Rebecca Adlington in the 800m freestyle in 8:14.63.

In the last event of the night, Frenchman Florent Manaudou denied a US clean sweep by taking the men's 50m freestyle in 21.34 seconds, edging American Cullen Jones into second in 21.54 and Brazilian world record holder Cesar Cielo third in 21.59.

The United States now leads the medals count with 43, including 21 gold. China is in second place with 20 gold, 13 silver and nine bronze after claiming two golds Friday.

Zhang Nan and Zhao Yunlei won the mixed doubles gold at the badminton tournament, beating Xu Chen and Ma Jin 21-11, 21-17 in the all-Chinese final.

Also, China is assured of the women's singles title, with top seed Wang Yihan and third seed Li Xuerui winning their respective semi-finals.

In men's singles, Malaysia's Lee Chong Wei set up an anticipated championship rematch with defending champion Lin Dan of China. Lee beat China's Chen Long 21-13, 21-14, and Lin overcame South Korean Lee Hyun-il 21-12, 21-10.

Chinese world number one Dong Dong broke down in tears as he snatched the Olympic men's trampoline title.

Guo Shuang gave China second silver medal in cycling events when she was narrowly beaten by Britain's Victoria Pendleton in the women's keirin, a day after she and teammate Gong Jinjie won the team sprint event only to be relegated soon after an "illegal changeover".

Germany's Miriam Welte and Kristina Vogel were crowned inaugural Olympic women's team sprint champions following the relegation of China.

But the Chinese cycling team appealed the ruling Friday. In an official statement, the Chinese team said: "Gong Jinjie and her teammate Guo Shuang beat the record twice, in the qualifying and the first round. In the final, Chinese team beat Germany with a result of 32.617, but was relegated to second place by the referee who did not show any video replay."

"Our gold was robbed," China's French coach Daniel Morelon said Friday.

In tennis, Maria Sharapova breezed into her first Olympic final as the 25-year-old Russian defeated compatriot Maria Kirilenko 6-2, 6-3 in the semifinal.

Sharapova could complete the "Super Slam" of titles in all four majors and the Olympic singles if she beats Wimbledon champion Serena Williams in the final. The American brushed aside world number one Victoria Azarenka 6-1, 6-2 in the other semifinal.

Seven-time Wimbledon champion Roger Federer is just one match away from his first Olympic singles title after edging out Juan Martin Potro of Argentina 3-6, 7-6 (7-5), 19-17 in four hours and 26 minutes, the longest three-set men's singles match in the Open era.

Federer plays local favourite Andy Murray for the gold, the Briton overcame Serb Novak Djokovic 7-5, 7-5 in exactly two hours.

On the first day of athletics action, Poland's Tomasz Majewski clinched the men's shot put gold with a throw of 21.89 metres. Germany's David Storl claimed silver with 21.86m and American Reese Hoffa bronze with 21.23m.

Ethiopia's Tirunesh Dibaba became the first woman to win the Olympic 10,000m final for the second straight time. She crossed the line in 30 minutes 20.75 seconds.