America's women left their great Jamaican rivals trailing to storm to gold in the Olympic sprint relay on Friday, running a perfect race to smash one of the oldest world records in the book.

On a dramatic night on the track, Ethiopia's Meseret Defar surged to victory in the women's 5,000 metres to deny her compatriot Tirunesh Dibaba a historic second double of Olympic distance titles.

And the Bahamas, silver medallists four years ago, ran down a weakened U.S. quartet in the home straight for gold in the 4x400m, denying the Americans an eighth successive Olympic title.

On a day when former drugs offenders won gold in the women's 1,500m and hammer throw and the men's 10km swim, there was news of two new doping suspensions in distance running.

Elsewhere, the Netherlands won the women's hockey tournament, Australia asserted their dominance in sailing, and Olympic minnows Colombia and Latvia won golds in BMX cycling.

The U.S. reigning Olympic basketball champions, featuring LeBron James and Kobe Bryant, set up a repeat of their 2008 final against Spain by brushing aside Argentina 109-83. Spain beat Russia 67-59.

The penultimate day of track and field competition in London brought high drama in the relays.

Bungled handovers had denied the American women 4x100m gold at the last three Games, but Tianna Madison, Allyson Felix, Bianca Knight and Carmelita Jeter combined slickly to run 40.82 seconds, beating East Germany's 1985 world mark by more than half a second.

Jamaica finished second in a national record, only 0.04 seconds outside the old world record of 41.37.

Jamaica and the United States have carved up all the sprint golds between them so far in London, and Jamaica's 100m bronze medallist Veronica Campbell-Brown praised her rivals.

"I feel females don't get as much respect as their male counterparts. We need to get more records ... The result was phenomenal," she said.

In the women's 5,000, Dibaba was unable to reproduce the scintillating last lap that won her the 10,000m a week ago.

Having failed to shake off her main rivals, the "baby-faced destroyer", winner of the 5,000 and 10,000 in Beijing, faded at the end to be outsprinted by Defar, the 2004 champion, and Kenyan world champion Vivian Cheruiyot.

Turkish gold

Asli Cakir Alptekin, who served a two-year doping ban from 2004 to 2006, won Turkey's first ever athletics gold in the 1,500, leading the field in a storming last lap after a painfully slow first 1,200m.

Russia's Tatyana Lysenko, who watched the 2008 Olympics on television while serving a two-year doping ban, won the women's hammer.

Mathew Kisorio of Kenya, the world's great middle- and long-distance power alongside Ethiopia, was confirmed to have tested positive for a banned substance in June.

Kisorio told German television that blood-doping and steroid use were widespread in Kenya, but officials dismissed the allegation while acknowledging that there had been other cases.

"We don't joke with doping matters. This year alone, we have banned four athletes," said David Okeyo, secretary general of Athletics Kenya.

French 5,000m runner Hassan Hirt failed a test for the banned blood-booster EPO (erythropoietin) prior to competing in London, a source with direct knowledge of the matter said.

France's 3,000m steeplechaser Nour-Eddine Gezzar had also been suspended for using EPO in the run-up to the Games.

Tunisia's Oussama Mellouli, who served an 18-month ban in 2006-2007 for using banned stimulants, won the men's swimming marathon through the Serpentine lake in Hyde Park to become the first swimmer to get medals in the pool and open water.

Earlier in the week, Victor Conte, convicted owner of a now-defunct laboratory at the centre of a global steroid scandal, said it was easy to cheat at the Olympics by using drugs.

The International Olympic Committee (IOC) dismissed his comments as being "like a poacher criticising a gamekeeper".

France's European champion Renaud Lavillenie produced an Olympic record jump of 5.97m to win gold in the men's pole vault, after Australia's defending champion Steve Hooker went out of the competition early on.

But there was better news for Australia in sailing, where they are set to finish as the leading country. They won their third gold in the men's 470 class, and look all set to win another in the women's Elliott 6-metre keelboat on Saturday.

Hockey double?

In hockey, the Netherlands beat world champions Argentina 2-0 in the women's final - and will go for the double when their men play Germany in what could be a classic final on Saturday.

Mariana Pajon, Colombia's flag bearer at the opening ceremony, won her country's first gold medal of the Games when she thundered to victory in the BMX cycling, where competitors race over bumps and around banked corners.

Latvia's Maris Strombergs, who cried when he first saw a BMX race at the age of five, remained the only men's Olympic champion in the discipline when he retained his title.

In handball, three-time men's silver medallists Sweden gave themselves a chance of a first Olympic gold by beating Hungary.

In the final they will meet France, the title holders, who beat twice winners Croatia in their semi-final.

The United States stood atop the overall medals table with 41 golds to China's 37.

The two have been neck-and-neck throughout London 2012 in the race for Olympic bragging rights. Whoever wins, the home nation will certainly be celebrating their best medals haul since 1908, when London first hosted the Games.

Britain's 25 golds puts them behind China in third place and easily surpassed their 2008 total of 19.

That golden glow has helped fuel the popularity of the Games among a public that has packed many venues and lifted athletes with deafening cheers.

IOC President Jacques Rogge gave the London Games a lavish endorsement, telling the city's Evening Standard newspaper: "The superlatives created here in London will live on long after the cauldron is finally extinguished.

"In the true spirit of Britain, huge crowds have cheered on not just their athletes but those of the world, and sent an echo that resonates in every home across the globe," he added.

Before the baton is passed to Rio de Janeiro, which hosts the first South American Olympics in 2016, the world will witness a closing ceremony celebrating British music, with the Spice Girls, The Who and Brian May among those set to perform.