The Czech Republic won the first gold of the Olympics on Saturday, dashing Chinese hopes for an early medal to cap a dazzling opening ceremony.
Katherine Emmons of the Czech Republic won gold in the women's 10m air rifle, with Chinese hopeful Du Li coming fifth.
Beijing is determined to stage an awe-inspiring Games that will underline its status as a new superpower, and would love to overtake the United States at the top of the medals table.
Seven golds are up for grabs on Saturday.
But the attention of many fans will be on American swimmer Michael Phelps, the lanky 23-year-old with a handlebar moustache aiming for an unprecedented eight golds.
He plunges into the shimmering new Water Cube aquatics centre for his heat in the 400 meters individual medley in the evening: the first of 17 starts in nine days as he tries to better Mark Spitz's record seven golds in 1972.
"I'm here having fun," said Phelps, who lowered the 400 meters medley world record for the seventh time in June but had fellow American Ryan Lochte less than a second behind.
A campaign to stamp out the use of performance-enhancing drugs claimed another victim, a Greek sprinter being sent home from the team for failing a earlier doping test, in an uncanny reminder of Athens in 2004.
Then two Greek sprinters, both major medals hope, were involved in a doping scandal that overshadowed the start of the Games. This time another sprinter, Tassos Gousis, is being sent home, Greek media reported.
Olympic chief Jacques Rogge used his speech at the opening ceremony to appeal to the better nature of the 10,500 athletes from 204 countries taking part in the Games, reminding them they were "role models for the youth of the world."
In case that doesn't work, he has also introduced tougher tests.
Several Greek athletes, including 11 weightlifters, a boxer and a swimmer have tested positive for banned substances this year after tougher controls by the Hellenic Olympic Committee.
Some of Russia's leading medal hopes have also been expelled or suspended in the past week after failed tests.
DEMONSTRATION OF CHINESE POWER
China opened the Olympics on Friday night with a glittering ceremony that celebrated its ancient history but also demonstrated its modern image and emerging superpower status.
Riding an economic boom, the Communist government of the world's most populous nation has spent $43 billion on the Games.
More than 80 world leaders, including President George W. Bush whose fellow Americans are increasingly nervous of China's global clout, joined 91,000 spectators for an opening show of fireworks, drums and dance at the Bird's Nest stadium.
"It was spectacular, really unbelievable, we liked it a lot," First Lady Laura Bush told reporters on a Saturday morning tour of the Forbidden City, former home to China's emperors.
But the spectacle was marred for some by the sight of goose-stepping soldiers raising the Olympic flag.
"The heavy presence of Chinese (People's) Liberation Army officers throughout the proceedings left many wondering exactly what image the hosts were intending to project to the international community," the Sydney Morning Herald said.
The hosts even fended off wet weather for the opening by firing 1,104 rain-dispersing rockets into the skies, the first time this technology has been used at such a high-profile event, state media reported.
But thundershowers were forecast on Saturday, and the Olympic flame burnt above the stadium in very hazy skies. Smog has been a feature of the run-up to the Games despite an $18 billion campaign to clean the skies around the city.
The Games have also been a lightning rod for critics of China's policies on Tibet and religious freedom, and despite a 100,000-strong security force in Beijing, small groups of foreign protesters have shouted or unveiled banners this week.
Hong Kong police threw two protesters out of the city's Olympics equestrian arena on Saturday, pouncing on them as they reached into their bag for a Tibetan flag they had smuggled in.
Three demonstrators who unfurled a Tibetan flag by the Bird's Nest on Friday night were also detained within seconds by police.
Beijing hopes the world will now focus on sport.
Boxing also starts on Saturday. Traditional power Cuba, who won five golds in Athens 2004, have been weakened by a string of defections of top fighters and face a stiff field.
Head coach Pedro Roque was confident though: "We have enough boxers for one, two or three teams."
Cyclists will be the first endurance athletes to test the impact of Beijing's pollution and heat in the men's road race winding from the ancient Forbidden City to the hilly Great Wall.
"This is the toughest course I have ever seen at a tournament event," said Netherlands coach Egon Kessel.
All eyes on the judo mat will focus on Japan's Ryoko Tani: the celebrity and super-mum wants a third straight Olympics gold.
(Reporting by Beijing Olympic bureau; Editing by Nick Macfie)
