Swimming legend Michael Phelps begins his campaign to become the greatest Olympian in history as the first full day of action of the London Games gets under way on Saturday.
Phelps, who has 16 career medals including 14 gold, is swimming seven events and needs just three medals to surpass Soviet gymnast Larisa Latynina's Olympic career record of 18.
The 27-year-old American is not the only superstar in action on Saturday with Wimbledon champions Roger Federer and Serena Williams starting their tennis bids at the All England Club.
Cyclist Mark Cavendish hopes to give the hosts a golden start in the men's road race while Chinese shooter Yi Siling is favourite to win the first gold of the Games' 302 on offer.
The eight-day swimming programme starts with a bang with Phelps and arch-rival Ryan Lochte on a collision course in the men's 400m individual medley.
Phelps' haul of eight gold medals from the Beijing Olympics four years ago included the 400m medley title, but he was beaten by Lochte, the reigning world champion, at the US trials.
Competition at the Aquatics Centre kicks off Saturday morning with the men's medley heats, and the final -- one of four -- is the first race of the evening session.
Phelps is aiming to become the first male swimmer to win a gold medal in the same individual event in three successive Olympic Games and will not surrender his crown without a fight.
"It's going to be a very challenging and exciting race, I have changed a few small things to see if it will help (since the US trials)," said Phelps.
Most interest centres on whether Phelps can repeat his golden Beijing form against the in-form Lochte, who took the 400m medley gold at last year's world championships, an event Phelps sat out.
On The Mall, Tour de France sprint king Cavendish looks to win the hosts' first gold medal of the Games.
Only six days after Cavendish played a role in Bradley Wiggins' historic yellow jersey triumph, the race's 23-times stage winner starts as the favourite for the 250km men's race.
Federer returns to Wimbledon, where he captured a record-equalling seventh title earlier this month, as the world number one begins his campaign to add singles gold to the doubles title he captured in Beijing in 2008.
He starts against Colombia's Alejandro Falla.
Serena Williams, twice a doubles gold medallist with sister Venus, faces Jelena Jankovic.
The 30th Summer Games, which features over 10,000 athletes from 205 nations, will see the first gold decided at the Royal Artillery Barracks where China's world number one Yi is favourite in the women's 10m air rifle.
Defending champion Pang Wei could make it a China double in the men's event.
Elsewhere, legally blind archer Im Dong-Hyun, who set the first world record of the Olympics on Friday, and then added another as South Korea broke the team record, targets gold.
There are also golds on offer in the women's weightlifting and men and women's judo.
Queen Elizabeth II declared the Games on Friday night before seven young athletes lit the cauldron at the Olympic Stadium at the end of an eccentric, humour-filled showcase devised by "Slumdog Millionaire" director Danny Boyle.
Britain's newspapers lavished praise on the spectacular four-hour long ceremony, watched by an estimated one billion TV viewers around the world.
The Times ran the headline "A Flying Start" on a souvenir wraparound photograph of the Red Arrows display team flying over the stadium while Rupert Murdoch's market-leading tabloid The Sun went simply with "Golden Wonder".
A budget of £9.3 billion ($14.5 billion, 12 billion euros) has been spent on bringing the Games back to London.
