Swimmer Michael Phelps won his 17th Olympic medal to take him closer to the all-time mark, but his US freestyle relay team were upstaged by France as records fell in the pool on Sunday's second day of competition at the London Games.
South Africa's Cameron Van der Burgh and American Dana Vollmer set world records in the men's 100 metres breaststroke and women's 100 butterfly, Van der Burgh denying Japan's Kosuke Kitajima in his bid to be the first male swimmer to win gold in the same event at three successive Olympics.
Cyclist Lizzie Armitstead won Britain's first medal of the London Games, a silver behind the Dutch favourite Marianne Vos in a nailbiting, rain-drenched women's road race.
The latest US basketball Dream Team played to the gallery as they cruised through their opening match against France, but there was an upset for another American gold medal favourite, gymnastics world all-around champion Jordyn Wieber, who failed to qualify for the individual Olympic final.
Overall, China took a commanding early lead in the rankings with 12 medals, six of them gold, ahead of the United States on 11 medals, including three golds.
Meanwhile organisers sought to quell growing frustration with empty seats among the tens of thousands of Britons who finished up ticketless in the pre-Games booking system.
Phelps won his first ever silver after swimming a storming second leg in the 4x100 freestyle relay to lift his overall medal tally to 17, just one shy of the all-time record held by Soviet gymnast Larisa Latynina.
But a flying anchor leg from France's Yannick Agnel snatched the gold from the fingertips of Phelps's team mate and great individual rival Ryan Lochte.
Australia, the fastest qualifiers and looking to notch a famous victory against their traditional rivals for pool supremacy, were soundly beaten into fourth.
Four years ago in Beijing Phelps won gold in each of the eight events that he swam. In London, after losing his 400 individual medley title to Lochte on Saturday, he has already tasted defeat twice in two days.
US swimmer Dana Vollmer ended a lifetime of frustration and battles with her health to win the 100 metres butterfly gold medal in world record time.
Swimming like a woman possessed, Vollmer sliced 0.08 seconds off a record set at the 2009 world championships in Rome before polyurethane bodysuits were banned.
Vollmer won a relay gold at Athens in 2004 a year after heart surgery. But she failed to qualify for Beijing in 2008 and did not return to form until she was diagnosed with an egg allergy and put on a special diet.
Cameron Van der Burgh also broke the world record, for the 100 breaststroke, to become the first South African man to win individual Olympic swimming gold.
His time trimmed 0.12 seconds off the record set by Australia's Brenton Rickard, also in Rome in 2009.
Japan's Kitajima, who won the breaststroke double at Athens in 2004 and Beijing four years later, was fifth, and will have to look to the 200 in London to try to make it three in a row.
There was a further pool gold for France when top-ranked Camille Muffat won the women's 400 freestyle ahead of Allison Schmitt of the United States and Britain's defending champion, Rebecca Adlington.
Britain's quest for its best ever medal haul had got off to a slow start when it failed to win one on the first day of competition.
But Armitstead got in ahead of Adlington to set the ball rolling on Day Two when she, Vos and Russia's Olga Zabelinskaya launched a gutsy breakaway in torrential rain 50 km from the end of the women's cycling road race.
Vos, the hot favourite, who won the points race on the track in Beijing but has come second in the last five world championship road races, made no mistake on the final sprint down the Mall in front of Buckingham Palace.
"The Olympics is different than the world championships. I knew it was a different race," Vos told a news conference. "You don't have to think about the years before."
Meanwhile China took its gold medal tally to six, twice that of the nearest challenger, the United States.
Guo Wenjun produced a near-perfect last shot to retain her Olympic title in the women's 10 metre air pistol shooting, while Wu Minxia and He Zi took their expected easy gold in the women's synchronised 3 m springboard diving.
The sight of rows of vacant seats at football stadiums, Wimbledon, the Aquatic Centre and beyond has angered Britons who tried and failed to buy tickets in the build-up to the Games after being told they had sold out.
More gaps were reported on Sunday, many at the equestrian eventing dressage despite the draw of Queen Elizabeth's granddaughter Zara Phillips making her Olympic debut.
Organisers launched an inquiry to nail down precisely who had not taken up their places and why, and filled many of the seats with soldiers taking a break from Olympic security duties.
"It's infuriating to see so many empty seats on TV. Surely it can't be beyond the organisers to allow real sports fans to fill them up on a first-come first-served basis?" said Ed Shorthose, a London-based father of two who had been trying for months to get tickets to see the Games.
South Korea's women extended their domination of Olympic archery by winning their seventh straight gold, although they needed a near-perfect nine from their last arrow to overcome China, who took their third successive silver.
The latest US basketball 'Dream Team', this time featuring LeBron James and Kobe Bryant, began their title defence with a 98-71 defeat of France, drawing 'oohs' from the crowd with no-look assists, thunderous dunks and sublime handling.
But there was no such joy for Jordyn Wieber, who fled from reporters as her dreams of being crowned all-around Olympic gymnastics champion were shattered.
A scrappy floor routine and a far-below-par balance beam display meant that it was her team mates Gabby Douglas and Aly Raisman who qualified for the individual final.
"She did not make any major errors but what can you do, sport is sport," said US team co-ordinator Marta Karolyi.
At Wimbledon, where rain forced the closure of the roof over centre court, women's second seed Agnieszka Radwanska slumped out in the first round to Julia Goerges of Germany.
Britain's Andy Murray beat Switzerland's Stanislas Wawrinka in straight sets but world number two Novak Djokovic of Serbia made a slow start against Italy's Fabio Fognini before winning 6-7 6-2 6-2.
Tiny Georgia added to its mighty judo tradition when Lasha Shavdatuashvili, the youngest competitor at just 20 and ranked only 32 in the world, won his country's third ever judo gold.
But proving the old Olympic adage that taking part is more important than winning was Hamadou Djibo Issaka, a rower from landlocked Niger.
Having taken up the sport only three months ago, the wildcard entrant was roared on by 20,000 spectators as he struggled to the finish line in the men's single sculls a full minute and 39 seconds after the heat winner.
"There are many people who want to start rowing because I have come to the Olympic Games," he said. "We will start when I get back. We just have to wait for the boats to arrive."