Ye Shiwen, who was in the center of doping speculation on Tuesday after her world record-breaking performance in the 400m IM on Saturday, won the 200m IM in an Olympic record time of 2:07.57.

Ye Shiwen wins the 200m IM in an Olympic record time of 2:07.57on Tuesday.

The 16-year-old Ye needed a typical strong final freestyle leg to overtake Australian Alicia Coutts, who produced a strong third lap on the breaststroke to momentarily take the lead.

"I didn't expect the others to swim so fast, I was surprised, but I couldn't lost the race," said Ye, who added the recent accusations of doping had not affected her.

Earlier on Tuesday, IOC communications director Mark Adams came to the defence of Ye, saying all medal winners are drug tested and there is no evidence against Ye.

"We have a very strong drugs testing program. And we're very confident that if there are cheats then we will catch them," said Adams.

"She is a victor. She is not a doper," he added.

American superstar Michael Phelps won two medals, including a relay gold, on Tuesday night to become the most successful Olympian ever.

Michael Phelps throws flowers to his mother after he wins the 4x200m freestyle relay gold on Tuesday.

A bittersweet silver in the men's 200m butterfly and the 4x200m freestyle relay gold lifted Phelps' career medal tally to 19, beating Russian gymnast Larisa Latymina's record of 18 medals.

Phelps' 19 Olympic medals included a record 15 gold, eight of them won in Beijing four years ago.

South Africa's Chad le Cos pulled off one of the biggest upsets in the Aquatics Center with a come-from-behind victory in the men's 200m butterfly final, thwarting Phelps' bid for his first gold in London.

Phelps was in the lead at every turn but Cos surged past the American at the finish to win in 1 minute 52.96 seconds. Phelps was just five-hundredths of a second behind, and Japan's Takeshi Matsuda grabbed bronze.

"He is a hard worker and he's a very talented kid," Phelps said of Cos.

Cos' triumph means Phelps missed out on the chance to become the first male swimmer to win the same event in three consecutive Olympics, but the Phelps did write his name into the Olympic record books when he returned a hour later to anchor the U.S. team to the 4x200m freestyle relay triumph.

"I thanked those guys for helping me get to this moment ," Phelps said after the race.

In the first final of the night, American Allison Schmitt won the 200m freestyle in a dominant fashion in an Olympic record time of 1:53.61. France's Camille Muffat got silver in 1:55.58, almost a body length behind, while Bronte Barrett of Australia was third.

Elsewhere, the duo of Chen Ruolin and Wang Hao won China's third diving gold medal in three events with a stylish victory in the women's 10-meter synchronized platform final.

Chen and Wang led from second dive to finish with a total score of 368.40 points, over 25 points ahead of their nearest rivals Paola Espinosa and Alejandra Orozco of Mexico.

"I wasn't nervous, the finals are a test of what we have trained for," said the 19-year-old Chen.

With three wins out of three events, the Chinese diving "Dream Team" are right on course to sweep all eight gold medals and improve on their performance in Beijing where they won seven.

Also on Tuesday, China secured its first table tennis gold at these Games after Ding Ning and Li Xiaoxia both reached the women's singles final.

Top seed and reigning world champion Ding defeated Feng Tianwei of Singapore 11-7, 11-4, 9-11, 12-10, 6-11, 11-6, before Li swept past Japanese Kasumi Ishikawa 11-5, 11-4, 11-13, 11-6, 11-7.

"I won't feel pressured because the gold medal is already ours. I'm going to show my best to the world," Li said of Wednesday's final.

Lei Sheng handed China its first fencing gold at the Games when he edged Egypt's Alaadldin Abouelkassem 15-13 in the final.

Despite his near miss from the title, Abouelkassem became the first African to make the podium in the sport.

"It's unbelievable, I really can't believe what I've done. It was very hard for me, but I did it," Abouelkassem said. "I'm the first African fencer who has won an Olympic medal and that makes me proud."

Also on Tuesday, China picked up its second gold in weightlifting when Lin Qingfeng finished a full 11kg clear of the field to win in the men's 69kg category.

The American women gymnasts delivered near-perfect routines to win the team title, their first Olympic gold medal since 1996. Russia claimed silver and European champions Romania took bronze.

The five-woman team of Gabrielle Douglas, Kayla McMaroney, Alexandra Raisman, Kyla Ross and Jordyn Wieber earned the highest scores in all disciplines but uneven bars for a winning total of 183.596 points.

Defending champions China finished just fourth.

By the end of the fourth full day of competition, China is on top of the medal table with 13 gold, 6 silver and 4 bronze, followed by the United States on 9-8-6 and France 4-3-4.