* Phelps qualifies last for medley final
* South Korean freestyle champion disqualified
* China takes first gold of Games in women's shooting
By Mark Trevelyan
LONDON, July 28 (Reuters) - China fired out a signal of their Olympic intent with the first gold medal of the London 2012 Games on Saturday in the shooting, while the host city warmed up to a Michael Phelps-Ryan Lochte showdown in the pool.
The U.S. team mates square off on the opening night at the aquatic centre, which staged early drama when Phelps only narrowly scraped through his heat, and 2008 Olympic champion Park Tae-hwan was disqualified in the 400 freestyle.
The 22-year-old, who won gold over that distance four years ago, came first but was ruled to have left the blocks a fraction too early. The South Korean team protested and lodged an appeal, and the sports governing body is deliberating.
China's Yi Siling became the first gold medallist of the Games when she won the 10 metre air rifle shooting - despite confessing to reporters: "For the first round and the last round I was very nervous and didn't know what I was doing."
Competition in badminton, archery, table tennis and judo also started early on a bright sunny morning in London.
After Friday night's opening ceremony, where Britain laid on a dizzying and sometimes eccentric extravaganza for the world, the host nation were in strong contention to win their first gold medal of the Games in the men's cycling road race.
A powerful team including Tour de France winner Bradley Wiggins was poised to set up world champion Mark Cavendish for a sprint finish down The Mall, the broad avenue leading to Buckingham Palace.
In rowing, the British pair of Helen Glover and Heather Stanning set a Games record in their heat, to confirm their status as favourites to win their country's first Olympic gold medal for a women's crew.
A celebration of the country's grandeur and quirky humour that lurched from the Industrial Revolution to the Beatles, the opening ceremony extended into the early hours and wowed the crowd of 60,000 in the stadium and a probable billion television viewers around the globe.
"A gigantic spectacle. What a show!" raved Germany tabloid Bild.
International Olympic Committee (IOC) president Jacques Rogge told the audience: "In a sense the Olympic Games are coming home tonight. This great, sports-loving country is widely recognised as the birthplace of modern sport."
On a darker note, Albanian weightlifter Hysen Pulaku became the first athlete to be ejected from the Games after testing positive for an anabolic steroid.
"Of course it is always a sad day when a cheating athlete is caught," said IOC spokesman Mark Adams. "I hope there will not be more."
Ireland's Olympic Council said it was investigating an allegation that one of its competitors at the Games had previously bet on an opponent to win an event in which they were both competing. It did not name the athlete or the sport.
More than 10,000 athletes from 204 countries will compete in 26 sports over 17 days of competition in the only city to have staged the modern Summer Games three times.
The biggest event of the first day is in the pool, where Phelps defends his 400 metres individual medley title against Lochte, the reigning world champion and favourite, in what is being billed as one of the great rivalries of the Games.
Phelps has 16 Olympic medals, 14 of them gold, and is bidding to become the most prolific medallist of all time by overhauling the record of 18 held by Soviet gymnast Larisa Latynina.
If he wins on Saturday, he will become the first man to capture three consecutive Olympic swimming titles in the same discipline.
But he was just millimetres away from making a shock early exit on the opening morning. A desperate lunge with his final stroke was enough to edge out Hungary's Laszlo Cseh by 0.07 seconds and give Phelps the eighth and last spot in the final.
"I didn't expect those guys to go that fast in the heats," said Phelps.
"I think the only thing that matters is getting a spot. You can't get the gold medal from the morning."
Lochte, who has exuded confidence this week, was third fastest overall, after Japan's Kosuke Hagino set the quickest time.
"It didn't feel so good, but that was my first race, and my first race is always the worst one," he said.