LONDON (Reuters) - With a historic sprint 'double-double' in the bag for Usain Bolt, Tirunesh Dibaba bids to provide another on Friday, when gold in the women's 5,000m would mean she had won both the longest track races at successive Olympics.
The Ethiopian retained her 10,000m crown a week ago with a scintillating last lap, demonstrating that she was back to her best after years of injury.
Bolt's time of 19.32 seconds in winning the 200 on Thursday night equaled the fourth fastest ever as he eased down in the last 30 meters, sensing that he was not on course to break his own world record. Silver went to his main rival and training partner Yohan Blake, and bronze to a third Jamaican, Warren Weir.
"After a rough season I came out here and did it," he said. I thought the world record was possible. I guess I was fast but not fit enough. I could feel my back strain a little bit, so all I did was to keep my form."
The successful defense of both his 100 and 200 titles was unprecedented, and confirmed him as the greatest sprinter in history.
If she can win on Friday, Dibaba will be emulating the 5,000/10,000m double of Finland's Lasse Viren in 1972/76.
Her main challenger in the 5,000 may be Kenya's Vivian Cheruiyot, who has played second fiddle to Dibaba for most of her career but herself won the 5,000 and 10,000 at last year's world championships.
Bolt's triumph capped a historic day when Kenya's David Rudisha broke his own 800m world record, Britain's Nicola Adams became the first woman to win an Olympic boxing title, and the United States held off a Japanese fightback to win their third successive women's soccer gold.
Jamaica's women try to keep their country's Olympic sprint magic flowing in Friday's 4x100m relay.
Women's double 100m champion Shelly-Ann Fraser-Pryce and third-placed Veronica Campbell-Brown will seek to repeat Jamaica's Beijing triumph against a U.S. quartet featuring 100m silver medalist Carmelita Jeter and 200m winner Allyson Felix.
The Jamaicans will be missing from the men's 4x400 after failing to qualify but the United States, seeking an eighth successive win in the event, are not as strong as usual and face a real battle to keep their streak alive.
They would have no chance at all but for Manteo Mitchell, who astonishingly secured a place in the final for his team by running through the pain of a broken leg.
Friday also sees medals on offer in the women's 1,500 meters, women's hammer and men's pole vault, while the heats of the men's 4x100 relay should give the fans plenty of excitement.
Thursday's sellout audience of 80,000 audience in the athletics stadium were given the rare treat of a world record in a middle distance final, as Kenya's David Rudisha became the first man to break one minute 41 seconds.
"I had no doubt about winning, but I was waiting for perfect conditions to break the record," he said, suggesting he might go even faster later in the season if conditions were right.
World record holder Ashton Eaton of the United States won the decathlon, comfortably ahead of compatriot Troy Hardee, and the Czech Barbora Spotakova claimed the women's javelin gold.
There was another American one-two in the triple jump, where world champion Christian Taylor produced this year's biggest leap to take gold ahead of Will Claye.
At Wembley, in the women's soccer final, two goals from midfielder Carli Lloyd ensured that the Americans avenged their defeat by Japan in last year's World Cup final. The 80,000 crowd was the biggest for a women's Olympic soccer match.
The U.S. also won their first women's water polo gold, beating Spain 8-5 in the final.
By the end of the day, the United States were on top of the medals table with 39 golds ahead of China on 37.
Saturday's women's basketball final will be contested by France and the U.S., who have not lost at the Games in 20 years, after they beat Russia and Australia respectively.
Three golds for the host nation Britain on Thursday - one for Adams with the other two in taekwondo and individual equestrian dressage - kept them in third place.
With 25 golds, they have already gone six better than in Beijing in 2008.
But Britain's men's field hockey hopes were dashed when the team were crushed 9-2 by the Netherlands in their semi-final. In the final, the Dutch will play the title holders Germany, who beat world champions Australia 4-2.
Across Afghanistan, people put aside war worries to crowd around televisions and even into cafes normally closed for the fasting month of Ramadan to cheer on taekwondo fighter Rohullah Nikpai, their country's first and only Olympic medalist.
Nikpai won bronze in the men's featherweight category in 2008, and rewarded the home fans by repeating the feat in London.
Germans Julius Brink and Jonas Reckermann became the first European team to claim men's beach volleyball gold by beating Brazilians Emanuel Rego and Alison Cerutti in three sets.
Belgian track cyclist Gijs Van Hoecke was sent home from the Games after photographs appeared in British newspapers of him apparently drunk and being carried into a taxi after a night out in London.
In a doping case dating back to 2004, American time-trial cyclist Tyler Hamilton will officially be stripped of his Athens Olympic gold medal on Friday after he admitted to doping, a source at the International Olympic Committee (IOC) said.
Retired Russian Viatcheslav Ekimov will move up to gold.
(Reporting by the Reuters Olympic team; Editing by Nigel Hunt)