London - American swimmer Ryan Lochte sunk record-chasing Michael Phelps on Saturday in a pulsating start to the Olympics while China's Sun Yang and Ye Shiwen wrote their name in the record books.
Lochte's 400m individual medley showdown with Phelps turned out to be a no-contest as he dominated to win in 4min 05.18sec, ahead of Brazilian Thiago Pereira and Japan's Kosuke Hagino, with Phelps back in fourth.
The loss is a setback for 16-time medallist Phelps, who memorably won a record eight titles in Beijing, and needs just three more medals to overhaul Soviet gymnast Larisa Latynina's all-time best of 18.
"It was just a crappy race," Phelps said. "I felt fine the first 200 and then I couldn't really go the last 100."
Phelps has another six events to go. But Lochte was not the only star of the first full day of action as Sun became China's first ever male Olympic champion in the pool, with a commanding swim in the 400m freestyle.
Sun's clash with champion Park Tae-Hwan was also much anticipated, but it almost didn't happen after the South Korean was disqualified from his heat for a false start, before being reinstated after an 11th-hour appeal.
Their race was a classic, with Sun gradually reeling in the leading Park before leaving him for dead over the closing stages with a time of 3:40.14. Park took silver with America's Peter Vanderkaay claiming bronze.
But the stand-out swim of the pool's opening night belonged to Ye, 16, who shattered the 400m medley world record with 4:28.43 -- more than a second faster than defending champion Stephanie Rice's time from Beijing 2008.
Ye swam a lightning closing freestyle leg as she overtook pace-setting Elizabeth Beisel and finished nearly two body-lengths in front. America's Beisel was second and China's Li Xuanxu third, with Rice joint sixth.
"I dreamed of winning the gold medal, but I never ever expected to break a world record. I'm overwhelmed," said Ye. "It is a big evening for Chinese swimming."
Australia won their first gold in the women's 4x100m relay, with Alicia Coutts, Cate Campbell, Brittany Elmslie and Melanie Schlanger beating out the Netherlands and teen star Missy Franklin's American team.
After Friday's lavish opening ceremony, it was a packed first day of full action with competition in 19 sports, from the far-flung rowing lake of Eton Dorney and across east London's Olympic Park.
Kazakh cyclist Alexandre Vinokourov shocked hosts Britain in the men's road race while Chinese world number one shooter Yi Siling had the honour of claiming the first of the Games' 302 golds at the Royal Artillery Barracks in the women's 10m Air Rifle.
Russia's Arsen Galstyan won the men's under-60kg judo and Sarah Menezes took Brazil's first Olympic gold in the sport, in the women's under-48kg.
But the story of the under-48kg was Hungary's Eva Csernoviczki, who bounced back from being strangled unconscious in the quarter-finals to claim an unlikely bronze.
In the men's cycling, Britain's Tour de France heroes Bradley Wiggins and Mark Cavendish were undone by a combination of tactical racing and some incisive, late attacks, finishing well off the podium.
"It just seems like the other teams are happy not to win as long as we don't win," grumbled British hope Cavendish.
South Korea enjoyed a golden start when sharpshooter Jin Jong-Oh won the Olympic men's 10m air pistol gold medal.
And New Zealand's Hamish Bond and Eric Murray set the third world record of the Games, in the men's pairs rowing.
South Korea had set new individual and team men's archery records on Friday thanks to the form of legally blind archer Im Dong-Hyun.
But they could not keep up their magnificent scoring and finished behind third in the team competition behind Italy and the United States.
Saturday also witnessed the first failed drugs test of the Games after Albanian weightlifter Hysen Pulaku was suspended for taking the banned steroid stanozolol - the same drug that cost Canada's Ben Johnson his 100m athletics gold at the 1988 Seoul Games.
Away from the action, organisers investigated why significant numbers of empty seats were seen at several venues, including the tennis and swimming, despite overwhelming pre-tournament demand for tickets.
"We're looking at this very urgently," Olympics minister Hunt told the BBC. "We want to make sure this kind of thing doesn't happen."
Sunday's second full day of action sees 14 gold medals up for grabs, with highlights including American swimmer Missy Franklin, competing in seven events in London, beginning her individual programme.