By Mark Trevelyan
LONDON (Reuters) - World champion Vivian Cheruiyot of Kenya begins her bid for a distance double when the athletics program kicks off on Friday in the 80,000-capacity Olympic stadium.
Ethiopian Olympic champion Tirunesh Dibaba, who has the fastest time of the year, is expected to be her main rival in a much-anticipated 10,000 meters final.
Cheruiyot also has her eye on the 5,000 next week as she attempts to replicate her double gold from last year's world championships.
A trio of Americans will seek to capture the men's shot put gold for United States for the first time since 1996.
Reese Hoffa, Ryan Whiting and Christian Cantwell, silver medalist in Beijing four years ago, set out to dethrone Olympic champion Tomasz Majewski of Poland with Germany's world title holder David Storl also likely to be in strong contention.
The women's heptathlon gets underway with a line up that includes 2008 champion Nataliya Dobrynska from Ukraine, world gold medalist Tatyana Chernova of Russia and British hopeful Jessica Ennis.
The seven-discipline event concludes on Saturday.
With the opening of the athletics, the jewel in the Olympic crown, excitement will begin to build towards Jamaican Usain Bolt's defense of his 100 title on Sunday and his 200 crown four days later.
In swimming, Michael Phelps will race his last individual Games event in the final of the 100 butterfly.
Missy Franklin, 17, chases her third gold medal in the 200 backstroke while Rebecca Adlington carries British hopes in the 800 freestyle, bidding to repeat her victory in Beijing.
The men's team pursuit and woman's keirin will fire up the crowd at the velodrome which saw on Thursday six world records, a double disqualification and team sprint gold medals for Britain's men and Germany's women.
The overall medals table is neck-and-neck after six days, with the United States having caught up China to stand on 18 golds each.
PHELPS WINS DUEL
Two days after breaking the all-time record for the most Olympic medals with 19, Phelps added a 20th - and his 16th gold - by winning the 200 individual medley.
In their final duel before Phelps is due to retire, he pushed fellow American and world champion Ryan Lochte into second place and became the first male swimmer to win the same individual event three times at successive Games.
United States also celebrated victories in the women's rowing eight and for 16-year-old Gabby Douglas in the all-around gymnastics where she edged out Russian Victoria Komova who was too upset to wear her silver medal.
"People keep saying I was the first black American to win the gold medal and I'm so honored," Douglas, nicknamed the Flying Squirrel, told reporters after claiming the biggest prize in women's gymnastics.
Black belt Vladimir Putin cheered Russia's Tagir Khaibulaev to the country's third judo gold.
In a scandal over match-throwing in the badminton tournament, disqualified Chinese Yu Yang announced she was quitting the sport.
"This is my last competition. Goodbye Badminton World Federation, goodbye my beloved badminton," Yu wrote on her microblog.
She was one of eight women, two each from China and Indonesia and four from South Korea, kicked out of the Games for playing to lose group matches in order to secure easier knockout opposition.
The badminton debacle has been among the few sour notes of a Games distinguished by enthusiastic crowds, dismal British weather and Phelps's remarkable feats.
In the rowing, Nathan Cohen and Joseph Sullivan won the double sculls for New Zealand on Dorney Lake, west of London.
Fellow Kiwis Eric Murray and Hamish Bond, unbeaten since 2009 and victors in the last three world championships, will seek to emulate them on Friday in the coxless pairs.
(Editing by Tony Jimenez)
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