The crowd cheered wildly as Carmelita Jeter crossed the line as the clock marked 40.82 seconds — well below East Germany's 41.37 record from 1985. Teammates Tianna Madison, 200-metre champion Allyson Felix and Bianca Knight gave the U.S. a big lead heading into the anchor leg by 100 silver medallist Jeter.
"I was already pointing at the clock, saying 'there it is!'" Jeter said after the race. "There was a cloud hanging over us with people saying 'they cannot do this, they are going to drop the stick,' but we did it."
Heading into the final weekend of the London Games, the U.S. tops both the gold and overall medals races after trailing the Chinese for most of it.
It was yet another remarkable night in the main Olympic stadium as double amputee Oscar Pistorius of South Africa ran his last race of these Olympics in the men's 4x400-metre final. The U.S. just missed that gold, however, which went to the Bahamas. Pistorius — the first amputee runner in track and field to compete at the Olympics — received the South African baton in last place and was last crossing the line.
The man known as "Blade Runner" because of his prosthetic carbon fibre blades came close to not running at all Friday after a Kenyan runner on Thursday knocked over South Africa's Ofentse Mogawane on the final bend in the second leg of the race.
But the judges later ruled that the Kenyan runner had cut across Mogawane, causing the collision, and advanced the South African team to the final anyway.
In other track finals, an Olympic record was set as France's Renaud Lavillenie won the pole vault gold medal with a games mark of 5.97 metres.
In the women's 5,000 metres, Meseret Defar beat fellow Ethiopian Tirunesh Dibaba to win the gold. Defar, the 2004 Olympic champion, overtook Dibaba in the final stretch and took the gold medal in 15 minutes, 4.25 seconds.
Later, Asli Cakir Alptekin of Turkey also crossed the line ahead of her teammate Gamze Bulut to win the gold medal in women's 1,500-meters. European champion Alptekin, who served a two-year suspension for doping after the 2004 world junior championships, won the gold medal in four minutes 10.23 seconds.
Russia's Tatyana Lysenko earned a gold in women's hammer throw.
Away from the track, the Netherlands had a 2-0 win over world champion Argentina to hold on to their women's Olympic field hockey title. In the bronze medal match, Britain won its first women's field hockey medal in 20 years with a 3-1 victory over New Zealand.
Earlier Friday, Mathew Belcher and Malcolm Page of Australia held off their British rivals to win the men's 470 class, the country's third on the English Channel at Weymouth, ensuring that the Australians will finish with more sailing golds than Britain.
"I suppose I am an old man now," the 40-year-old Page said. "I have been campaigning in 470s for 15 years. To go out like this is incredible."
Sailing is just about the only place where Australia is excelling, particularly over the host country. After surprisingly winning just one gold medal in the swimming pool — in a women's relay — the games were an early disappointment for a team hoping to finish in the top five in the gold medal race.
They won't achieve that, but gold medals to 100-metre hurdler Sally Pearson and cyclist Anna Meares, along with the triple gold performance from its sailors in the past five days have taken some of the sting out of what has been an under-par games for Australia.
Most depressingly for Australia, its seven gold medals overall have been dwarfed by the 25 — and counting — won by their traditional and often bitter sporting rivals from Britain.
In a later race at Weymouth, Australia's trans-Tasman neighbour New Zealand won gold in the women's 470 class. Jo Aleh and Olivia Powrie clinched the Kiwis' second sailing medal and fourth overall.
Maris Strombergs of Latvia won his second straight Olympic gold medal in BMX, taking the lead out of the starting gate and never relinquishing it. Strombergs won the inaugural competition at the Beijing Games, but has struggled with injuries the past of couple years.
Carlos Mario Oquendo Zabala made it a good afternoon for Colombia with his bronze. His teammate Mariana Pajon — the flag bearer for Colombia in the opening ceremony — won gold in the women's race earlier in the day.
Squel Stein of Brazil crashed heavily during the semifinals of the race and was carried off the course on a stretcher.
At a murky Serpentine Lake in London's Hyde Park, Ous Mellouli showed his versatility in the water, winning the 10-kilometre open water race less than a week after taking bronze in the 1,500 in the Aquatic Centre pool, the first swimmer to achieve that feat at the same Olympics.
It was the second gold of Mellouli's Olympic career, having won the 1,500 at the 2008 Beijing Games.
He overcame shoulder and elbow injuries before the games, plus a virus two days ago. Now, he's considering retirement.
"Only those close to me know how much I struggled to get here today," Mellouli said. "I don't think there's a better way to go out than this. I can just leave it all behind and have no regrets."
Russia won the synchronized swimming team final, giving the country its fourth consecutive gold medal in the event. China and Spain took the other podium spots, leaving Japan without a medal in synchro swimming for the first time since the sport was added to the Olympics in 1984.
AP sports writer Dennis Passa contributed to this story.