Greece's two top sprinters pulled out of the Athens Games on Wednesday and apologised over a drugs drama that besmirched the spiritual homeland of the Olympics.

It was the biggest drugs scandal to hit the Olympic movement since 100 metres gold medallist Ben Johnsons's ignominious exit from the Seoul Games in 1988 over a positive test for steroids.

• India at the Games on Wednesday

Greek Olympic 200 metres champion Costas Kenteris, a national hero dubbed "Greece Lightning," said he was withdrawing "out of a sense of responsibility".

"I am adamant, I was never notified to go to the Olympic Village to take the test."

"Over the last years, I have gone through over 30 tests with no problems," he added, referring to his missed eve-of-Games test last Thursday.

Katerina Thanou, silver medallist at the Sydney Games, said: "I want to apologise to the Greek people that I will not be at the Games, that I will not manage to race, and that is why I handed my accreditation into the IOC today.

"It is very hard for an athlete to withdraw from the Games especially when those Games are at home."

Their controversial coach, Christos Tzekos, also withdrew but insisted: "I don't feel I have made any mistakes."

The six-day scandal angered and shamed Greeks. Government spokesman Thodoris Roussopoulos said: "It creates a bad image of the country, not only locally but on a world scale."

The timing of their decision could not have been more ironic.

It came as the Games returned to their spiritual homeland with the staging of the shot put at Ancient Olympia, birthplace of the Olympics.

However, drugs still kept pushing sport from the headlines when world 100 metres champion Torri Edwards's appeal against a two-year drugs ban was dismissed by the Court of Arbitration for Sport (CAS), ending her bid to compete at the Olympics.

But at least the swimming pool produced an evening of nerve-tingling competition that had the crowd on its feet.

U.S. teenager Michael Phelps powered his way to two more golds, setting a Games record in the 200 metres butterfly and helping his team to beat Australia in the 4x200 freestyle relay.

The 19-year-old took his tally to three golds and two bronzes and with three events still to go at the Athens Games, he now seems certain to become the first swimmer to win eight medals at a single Olympics.

"It was probably the most exciting race I've ever been part of," Phelps said after the battle with arch-rival Ian Thorpe's Australians in the relay that was a shining example of what sport is all about.

KILLER SHARK

After Australian Thorpe cut through the water like a killer shark in hot pursuit of its victim, American Klete Keller swam the race of his life to hold off the final challenge.

"It is an out-of-body experience, it's so exciting," Keller said. "It's kind of like you have no mind at all because it's all a blur."

Tennis produced one of the biggest shocks of the Games.

World number one Roger Federer's top target for the year -- an Olympic gold medal -- was taken away from him on what he called a "terrible day."

Despite 2004 Grand Slam wins at the Australian Open and Wimbledon and a soaraway lead at the top of the world rankings, the Swiss crashed out of the singles to the 79th-ranked Czech Tomas Berdych 4-6, 7-5, 7-5 in the second round.