LONDON Black belt Vladimir Putin cheered a Russian judoka to a gold medal at the Olympics on Thursday, and American Michael Phelps hit new heights by becoming the first male swimmer to win the same event at three successive Games.
The futuristic velodrome witnessed six world cycling records, a double disqualification and golds for Britain's men and Germany's women in the team sprints.
Elsewhere, a 'play-to-lose' badminton scandal took a new twist when a disqualified Chinese player said she was quitting the sport.
Controversy also struck in boxing. A Turkmen referee was expelled for failing to stop a bout in which a fighter was knocked down six times, and an Angolan coach was deemed a "plonker" by his team chief for failing to present their only fighter for a weigh-in, thus getting him disqualified.
It was Russian President Putin who staged one of the day's most emphatic victory celebrations, leaping to his feet with both fists aloft when his countryman Tagir Khaibulaev defeated a Mongolian opponent to win Russia's third judo gold.
Putin, who cultivates a macho image based partly on his skills on the mat, slapped the victor repeatedly on the back and grabbed his cheeks with both hands.
In buoyant mood, he went on to suggest to Russian news agency Interfax that members of female punk band Pussy Riot, on trial for protesting against him in a Moscow cathedral, should not be judged too harshly.
Prime Minister David Cameron watched the judo with Putin and had reasons of his own to celebrate, as Britain rose to fifth in the medals table with golds in the men's cycling, double trap shooting and canoe slalom double.
In the scandal over match-throwing in the badminton tournament, disqualified Chinese Yu Yang announced she was quitting the sport in anguish.
"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, who were kicked out of the Games for playing to lose group matches in order to secure easier knockout berths.
The badminton debacle has been among the few sour notes of a Games distinguished by enthusiastic crowds, dismal British weather and the historic accomplishments of U.S. swimmer Phelps.
Two days after breaking the all-time record for the most Olympic medals with 19, he added a 20th - and his 16th gold - by winning the 200 meters individual medley.
In their final duel before Phelps is due to retire, he pushed compatriot and world champion Ryan Lochte into second place.
Two female swimmers, Australia's Dawn Fraser and Hungary's Krisztina Egerszegi, had won the same individual event at three Games, but no man had previously achieved the feat.
It was a first individual gold of the London Games for Phelps, no longer the all-conquering figure who won an unprecedented eight gold medals four years ago in Beijing.
The United States also celebrated victories for its women's rowing eight and for 16-year-old Gabby Douglas in the all-around gymnastics, where she edged out Russians Victoria Komova and Aliya Mustafina.
"The all-round matters to me. People keeping saying I was the first black American to win the gold medal and I'm so honored," Douglas, nicknamed Flying Squirrel, told reporters after claiming the biggest prize in women's gymnastics.
For the first time at these Games, the Americans drew level in the overall medals table with China, on 18 golds each.
China has 34 medals in all, including 11 silver and five bronze, while the U.S. has 37, with nine silver and 10 bronze.
In the velodrome, dubbed the Pringle for its resemblance to a curvy potato snack, Britain's men beat France and broke the world record in the team sprint final.
"We gave it our all and it worked out," said Chris Hoy after picking up his sixth Games medal and fifth gold.
The Chinese and British women had also set world records. But the latter, strong medal contenders, were disqualified after Victoria Pendleton went too early on a change-over with team mate Jessica Varnish.
China were relegated for a takeover infringement in the women's final, ending with the silver medal as the German team celebrated their promotion to gold.
(Additional reporting by Alison Williams, Martyn Herman, Maria Golovnina, Ian Ransom, Julien Pretot, Mark Meadows, Kate Holton, Paul Majendie, Padraic Halpin and Michael Martina in Beijing, editing by Peter Millership, Jason Neely and Ken Ferris)