LONDON - American swimmer Michael Phelps won the men's 100m butterfly on Friday for his 17th Olympic gold and 21st medal overall, as the United States overtook China on the top of the medals table thanks to a gold rush in the pool.

Phelps clocked 51.21 seconds for the 100m title, adding to his victories earlier in the 200m IM and 4x200m freestyle relay.

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

Michael Phelps of the US celebrates with his gold medal at the men's 100m butterfly victory ceremony at the London 2012 Olympic Games at the Aquatics Center, Aug 3, 2012.[Photo/Agencies]

Until Thursday no man had won an Olympic swimming title in three separate Games, Phelps ended that record with his win in the 200-meter 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 a bigger winning margin than the last two combined," said the 27-year-old Phelps, who has announced to retire after the London Games.

On Sunday, Phelps will take part in his last race - 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.

Missy Franklin of the US poses with her gold medal after winning the women's 200m backstroke final with a world record during the London 2012 Olympic Games at the Aquatics Center, Aug 3, 2012.[Photo/Agencies]

Coventry was in the race too, but was unable to make the podium.

"I knew I was just going to take it out and have fun and that's what I did. I am the happiest girl alive," said Franklin.

With the women's 4x100m medley to be contested on 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 favorite 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 gold on Day 7.

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.

Gold medalists China's Zhang Nan (L) and Zhao Yunlei pose for media during the victory ceremony for the badminton mixed doubles event at the London 2012 Olympic Games at the Wembley Arena, Aug 3, 2012. [Photo/Agencies]

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

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

"I'm really happy that I'm going to meet my old opponent," said 28-year-old Lin. "We are the same age and we get to play at the final of the Olympics. It's really good as it shows that we have not been knocked out by time."

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