BEIJING, Aug 12, 2008 (AFP) - US swimmer Michael Phelps joined an elite list of Olympic greats Tuesday becoming only the fifth competitor in history to win nine gold medals.

Phelps added his name to the prestigious group of Paavo Nurmi, Carl Lewis, Mark Spitz and Larysa Latynina when he won the men's 200m freestyle with a world record swim for his third gold medal in Beijing.

He appears destined to become the greatest Olympian as he continues his quest for an unequalled eight gold medals in one Games here and he said the toughest three races were behind him.

Ahead lie the 200m individual medley, 200m butterfly, 100m butterfly, 4x200m free relay and 4x100m medley relay.

"That's great," said Phelps as he emerged from the water after leading all the way in the 200m freestyle final to post a new world record of one minute 42.96.

"I just wanted to be out on my own which I had done by the 100 metres mark, that was my goal," Phelps said.

"I was out in open water and I was in the middle, which makes it difficult for the other guys to see me."

Phelps freestyle victory launched a dominant morning for the United States in the pool.

Aaron Peirsol lowered his own world record in winning the men's 100m backstroke, setting a new mark of 52.54sec, and Natalie Coughlin defended her women's 100m backstroke crown.

Australian Liesel Jones broke the US stranglehold when she won the women's 100m breaststroke title.

China lead the medals table with 10 gold, ahead of the United States on six and South Korea with five as the leading three shared all the early medals on Tuesday.

The hosts added to their tally when their men's gymnastics team, featuring three world champions, knocked back challenges from defending champions Japan and the United States.

Jin Jong-Oh picked up South Korea's fifth gold winning the men's 50m Pistol from Kim Jong-Su of North Korea.

Other gold medals are being contested in canoeing, synchronised diving, equestrian, fencing, judo, weightlifting and wrestling.

Germany are vying for their first gold at the Games in Hong Kong where they are leading contenders on the closing day of the team and individual sections of the three-day eventing competition.

Neither Brazil nor France have struck gold yet in Beijing but that could change on Tuesday.

France's Lucie Decosse is a strong prospect in the women's -63kg as is Brazil's Tiago Camilo in the men's -81kg division.

Further overnight rain improved conditions for outdoor Olympians, easing the smog over Beijing, patches of blue sky were visible and the midday temperature was an acceptable 27 degrees Celsius (81 Farenheit).

At the tennis venue, the Williams sisters continued their march with overwhelming second round wins.

Serena needed just 44 minutes to dispatch Australia's Samantha Stosur and Venus and was on court only slightly longer in easily beating Iveta Benesova in straight sets.

Sixth seed Russian Dinara Safina is also through to the third round after being taken to a first set tie-break she made no race of the second set to beat Spain's Maria Jose Martinez Sanchez (ESP) 7-6 (7/3), 6-1.

However, Daniela Hantuchova of Slovakia, the 10th seed, lost to Danish teen Caroline Wozniacki 6-1, 6-3.

Incoming men's number one Rafael Nadal will later face Australia's Lleyton Hewitt, who last occupied the top ranking in June 2003.

Kobe Bryant and the US all-star basketballers are back in action as well hoping to follow up their big win over China with a victory over Angola.