LONDON — America's women stormed 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 meters to deny her compatriot, Tirunesh Dibaba, a historic second double of Olympic distance titles.

And the Bahamas, silver medalists 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.

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 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 behind the old world record of 41.37.

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

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

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.

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

The U.S. 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.