Olympic 100 freestyle champion Pieter van den Hoogenband and world champion Alexander Popov both foundered in the heats of the men's 50 metres freestyle in a major surprise in the Olympic swimming pool on Thursday.

Van den Hoogenband, who had found it hard to sleep after retaining his 100 freestyle title on Wednesday, was unable to get his mind on the job and finished 17th overall in 22.56 seconds, while Popov, appearing in his fourth and last Olympics at the age of 32, was joint 18th in 22.58.

The top 16 qualified for the evening's semi-finals and the pair finished respectively 0.03 and 0.05 seconds behind the slowest qualifier.

"I was so not-focused. I had four hours' sleep. I was watching the ceiling the whole time. I went out on the balcony. I was so relieved," the 26-year-old Dutchman said.

He said people had been congratulating him all day, in the athletes' village dining-hall and on the bus to the pool. "Then it was, hey guys we have to swim a 50. I walked to the blocks and said 'focus, focus, focus', then boom, it was gone," he said.

But Van den Hoogenband, bronze medallist in the 50 at the 2000 Olympics, was far from upset, having achieved his main goal of retaining the 100 freestyle crown. "Yesterday I was so, so happy. I don't care about the 50," he said.

Michael Phelps, for once found himself not the centre of interest as he opened a busy day by qualifying comfortably for the evening's 100 butterfly semi-finals, winning his heat in the third-fastest aggregate time of 52.35.

Fellow American Ian Crocker, who beat Phelps to gold in last year's world championships, and world bronze medallist Andriy Serdinov of Ukraine were quickest overall in 52.03 and 52.05 respectively.

Phelps was aiming for his fourth title in the evening session in the 200 individual medley, having won gold in the 400 individual medley, 200 butterfly and 4x200 freestyle relay and bronze in the 4x100 freestyle relay and 200 freestyle.

Van den Hoogenband, who lost his 200 freestyle title to Ian Thorpe on Monday, finished seventh in his heat behind 16th and slowest qualifier Lyndon Ferns of South Africa.

Popov, eliminated in the semi-finals of the 100 freestyle on Tuesday, finished equal third in his heat, a sad end to his last individual race in a phenomenal career going back to the 1991 European championships in this city.

Gary Hall Jr clocked far and away the fastest aggregate time of 22.04 at the start of his defence of the title he shared at the last Olympics with fellow American Anthony Ervin.

Popov, who achieved a unique Olympic sprint freestyle 'double double' at the 1992 and 1996 Games, regained his world titles at both distances in Barcelona last year.

Seventeen-year-old Laure Manaudou of France, who won the 400 freestyle and took bronze in the 100 backstroke, targeted a second title as she led the way in the women's 800 metres freestyle heats in eight minutes 25.91 seconds.

Commonwealth champion Rebecca Cooke of Britain won her heat in the second-fastest overall time of 8:28.47 but there was no place in Friday's final for Germany's Hannah Stockbauer, who achieved a unique distance freestyle treble at the 2003 world championships.

Stockbauer, who also failed to negotiate the 400 freestyle heats successfully, was out of the picture, 14th overall. Newly crowned 200 freestyle champion Camelia Potec went out 16th overall but she is more of a 200 and 400 swimmer.

European champion Stanislava Komarova of Russia led the way in the women's 200 backstroke heats in 2:10.71. World champion Katy Sexton of Britain qualified eighth overall in 2:13.25.

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