Phelps makes history with eighth gold

On the final day of the swimming competition, there were also golds for Germany's Britta Steffen, Tunisian Oussama Mellouli and the Australian women's 4x100 medley team.

In athletics, Constantina Tomescu of Romania raced away from the field to seize gold in the women's marathon as world record holder Paula Radcliffe failed to win a medal.

Phelps' eighth gold, achieved with the US men's 4x100m medley team in world record time, saw him become the most successful athlete at an Olympic Games, breaking Spitz's record of seven golds at the 1972 Olympics in Munich.

"I'm lost for words. My team-mates were amazing. These guys made it possible. The relay really made it possible. It shows how much teamwork and togetherness we have," he said after the race.

In the first swim of the morning, Steffen ensured herself the sprint double, winning in Olympic record time of 24.06 seconds, a day after striking gold in the 100m freestyle.

Silver went to US veteran Dara Torres, who at 41 had hoped to become the oldest swimmer ever to win an Olympic gold. Her time of 24.07 seconds, was just one-hundredth slower than Steffen. Australian Cate Campbell took bronze in 24.17.

The German gave much of the credit for her performance to her psychologist, who was among the spectators in the Water Cube.

"I really worked a lot with my psychologist. When I was on the blocks this time I didn't feel like everyone else was better than me," the 24-year-old said.

In the next race Tunisian Oussama Mellouli denied Australian Grant Hackett a place in the history books as he won the Olympic gold medal in the men's 1,500m freestyle in a time of 14 minutes 40.84 seconds.

Hackett was attempting to become the first swimmer to win the 1,500m three times in a row. He won silver in 14:41.53, while Canadian Ryan Cochrane took bronze in 14:42.69.

Mellouli only returned from a lengthy doping ban earlier this year after having lost the gold and silver medal he won at the world championships in Melbourne in 2007.

The Australian women's 4x100m medley relay team shaved 3.05 seconds off their own world record when they won in 3:52.69. The US took silver in 3:53.30, while bronze went to China in 3:56.11.

Australian Jessicah Schipper said the team had gone into the race believing they could break the world record. "It's great to get a world record and by three seconds," she said.

Torres swam in the US team just 37 minutes after her freestyle silver. The relay gave her her third medal in Beijing and her 12th overall, equalling Jenny Thompson's women's record.

"It's an awesome feat because she is the most decorated swimmer," the mother-of-one said.

In the final race of the Olympic swimming competition, the US men's 4x100m medley team won in 3:29.34, beating their own world record from 2004 by 1.34 seconds. Silver went to Australia, while Japan took bronze.

It was the 25th world record to fall in the Water Cube.

The first gold medal of the day went to marathon runner Tomescu, 38, who ran away from her rivals at the halfway mark and never looked back en route to victory in 2 hours 26 minutes 44 seconds.

The reigning world champion Catherine Ndereba of Kenya took silver, as she did in Athens four years ago, while bronze went to China's Zhou Chunxi in 2:27.07.

Radcliffe, who was recovering from a stress fracture in her leg, flopped again at the Olympics after failing to finish in Athens 2004. She suffered cramps and came in more than six minutes behind in 23rd place, her worst ever marathon result.

The 2005 world champion called the race "one of the most frustrating" of her life and admitted she was "taking a gamble" when she decided to run.

Great Britain took the first sailing Olympic gold on offer when Sarah Ayton's crew won the yngling class ahead of the Netherlands and Greece in strong 30-knot winds in Qingdao.

Chinese marksman Qiu Jian won the men's 50-metre rifle three positions, beating silver medallist Jury Sukhorukov of Ukraine and Slovenia's Rajmond Debevec, who took bronze.

In the fifth doping case of the Games, Olympic 400-metres hurdles champion Fani Halkia of Greece tested positive for steroids just hours before she was due to compete.

Greek Olympic officials said Halkia was on her way back home after she was caught at an out-of-competition test on August 10 using the banned substance methyltrienolone.