American swimming great Michael Phelps looks to win his opening medal of the London Olympics on Sunday after suffering his first finish outside the top three in a Games final since he was 15.
The US face a tough task in the 4x100 metres freestyle relay against an Australian team boasting the fastest two men in the world.
But there should be a medal of some colour for Phelps, who is bidding to add three to his tally to overtake Soviet gymnast Larisa Latynina's record haul of 18.
Phelps must bounce back from a disappointing fourth place in the 400 individual medley in a race won by compatriot Ryan Lochte, who now appears to have displaced his long-time rival as the best all-round swimmer in the world.
"When I touched the wall I guess I was in shock. I guess I still am," Lochte said after winning one of the most eagerly awaited duels of the Games.
"I trained my butt off for four years, I just feel it inside my gut that this is my year."
It was the first time Phelps had missed out on a medal at the Olympics since he was a 15-year-old at Sydney in 2000.
Having won a record eight golds in Beijing four years ago, on Saturday he could have become the first male swimmer to win the same event at three successive Games. That honour could now go to Japan's Kosuke Kitajima in the 100 breaststroke.
Kitajima won the 100 and 200 breaststroke double at Athens in 2004 and Beijing four years later. He qualified for Sunday's final sixth fastest overall, with South Africa's Cameron van der Burgh setting the fastest time.
Like Phelps, host nation Britain are still seeking their first medal after world champion Mark Cavendish was outmanoeuvred and upstaged in the cycling road race by Kazakhstan's Alexandre Vinokourov.
Their best hope is in the pool where Rebecca Adlington defends her 400 freestyle title against Italian glamour girlFederica Pellegrini and world No 1 Camille Muffat of France.
But Britain also have chances to make amends in the women's cycling road race where holder Nicole Cookefaces Italian world champion Giorgia Bronzini and Dutchwoman Marianne Vos, who is hoping finally to land gold after five consecutive world championship silvers.
British fans have been out in force, giving a rock star reception to every appearance of a Team GB athl e te.
"They've probably never seen me before, but as soon as they see a GB shirt coming out, they start screaming," said Paul Drinkhall, Britain's top men's table tennis player, who rewarded fans by defeating Kuwait's Ibrahem Alhasen in the first round.
However, despite the clamour for tickets over recent months, the London Organising Committee of the Olympic Games was investigating why there were scores of empty seats in venues on Saturday, including Wimbledon and the aquatics centre.
LOCOG said in a statement: "Where there are empty seats, we will look at who should have been sitting in the seats a nd why they did not attend. Early indications are that the empty seats are in accredited seating areas, but this is day one an d our end of day review will provide a fuller picture."
LOCOG declined to provide a figure for the number of people in the park on Saturday or how many tickets had been sold but said that 11 million people would attend the Games.
"It is a shame this happened but we are going to do everything we can to make sure we fill up those stadia," Culture Secretary Jeremy Hunt, the Br itish mi nister responsible for the Olympics, told the BBC.
"I was at the Beijing G ames in 2008 and one of the lessons we took away from that was that full stadia create the best atmosphere, it's best for the athletes, it's more fun for spectators an d it has been an absolute priority."
The first full day of competition belonged to China , which was propelled to the top of the medals table in Beijingin part because of the home support. The team took four golds on Saturday including two imperious performances in the pool.
Sun Yang powered to their first male swimming gold in the 400 freestyle and 16-year-old compatriot Ye Shiwen won the women's 400 individual medley, smashing the world record by more than a second in the process.
Ye unleashed an incredible sprint over the concluding freestyle leg to surge clear of the favourite, Elizabeth Beiselof the United States.
In doing so she became the first woman to break a long-course world record since polyurethane bodysuits, which boosted buoyancy and triggered a slew of quickfire times, were banned in 2009.
China's Yi Siling had already become the first gold medallist of the Games in the 10-metre air rifle while compatriot Wang Mingjuan extended a 10-year unbeaten international record to win the women's 48-kg weightlifting crown.
Italy were second in the medals table with golds in archery and fencing.
Their men's archery team beat the top-ranked United States by a single point on the last arrow of the final and the fencers swept all three medals in the women's individual foil.
China look certain to land another gold on Sunday in the women's synchronised three-metre springboard diving final.
The Chinese dominate world diving and few would bet against victory for He Zi and Wu Minxia.
Day Two also sees the latest incarnation of the US basketball "Dream Team", this time featuring LeBron James, Kobe Bryant and Kevin Durant, beginning their title defence against France.
Tennis world No 2 Novak Djokovic of Serbia begins his quest for singles gold against Italy's Fabio Fognini.
Britain's Andy Murray returns to the court where he lost the Wimbledon final to Roger Federer this month for a first-round match against Switzerland's Stanislas Wawrinka.
Federer survived a scare in his opening Olympic singles match against Colombia's Alejandro Falla on Saturday before prevailing 6-3 5-7 6-3.
Serena Williams also breezed past Serbia's Jelena Jankovic in straight sets, with US First Lady Michelle Obama cheering her on.