(Adds details, quotes)
* Public anger over empty seats at some venues
* Many were told months ago tickets had sold out
* China tops medals table with six golds
* Host nation wins first medal after disappointment
By Karolos Grohmann and Mike Collett-White
LONDON, July 29 Organisers sought to quell growing public frustration on Sunday over empty seats across venues at the London Olympics, where China took a commanding early lead in the medals table and host nation Britain also got on the board.
The sight of rows of vacant seats at football stadiums, Wimbledon, the aquatic centre and beyond has angered Britons who tried and failed to buy tickets in the build-up to the Games after being told they had sold out.
More empty seats were reported on Sunday including at the equestrian dressage at Greenwich Park, despite the draw of Queen Elizabeth's granddaughter Zara Phillips making her Olympic debut.
Heavy rain after a hot, dry spell also put a dampener on outdoor events on the second day of full sporting contest, as did the announcement that Uzbek gymnast Luiza Galiulina was provisionally banned from the Games for a positive drugs test.
Olympic organisers launched an urgent inquiry into the seating fiasco to nail down precisely who had not taken up their places and why.
"It's infuriating to see so many empty seats on TV. Surely it can't be beyond the organisers to allow real sports fans to fill them up on a first-come first-served basis?" said Ed Shorthose, a London-based father of two who had been trying for months to get tickets to see the Games.
London organising committee chairman Sebastian Coe told reporters he thought the problem would resolve itself over time.
"I don't think this is going to be an issue, certainly it's not going to be an issue right through the Games," he said.
The embarrassment took some of the shine off the Games, where sport has begun in earnest after an exuberant opening ceremony on Friday night which thrilled Britain but also baffled much of the world because of its arty eccentricity.
Lizzie Armitstead won Britain's first medal of the London Games - a silver - in the women's cycling road race although the hosts had hoped for more. Dutch favourite Marianne Vos, runner-up at the last five road race world championships following her 2006 win, took the gold.
Overall, China had a commanding early lead in the rankings with nine medals, six of them gold, on the second full day of competitive sport at the July 27-Aug. 12 Games.
Guo Wenjun produced a near-perfect last shot to retain her Olympic title in the women's 10 metre air pistol shooting in a topsy-turvy final of nerve-jangling action, beating out France's Celine Goberville, while Wu Minxia and He Zi took an easy gold in the women's synchronised three metre springboard diving competition with an inward 2-1/2 somersault.
On Saturday, China's Yi Siling was the first gold medallist of the Games in the 10-metre air rifle and compatriot Wang Mingjuan extended a 10-year unbeaten international record to win the women's 48-kg weightlifting crown.
Chinese swimmers Sun Yang and Ye Shiwen also took gold on Day One, with 16-year-old Ye wiping more than a second off the world record in the women's 400 metre individual medley final.
Sun, who became the first Chinese man to win an Olympic swimming title when he took gold in the men's 400 freestyle, is overwhelming favourite to win the 1500 and is also targeting the 200, where he will square off against American Ryan Lochte.
Lochte grabbed the headlines on Saturday by eclipsing compatriot Michael Phelps in the 400 individual medley final and replacing him as the world's best all-round swimmer.
Lochte already has three gold medals from his two previous Olympics but is primed for a bigger haul this time with three more individual events and at least one relay still to come.
"I'm ready to rock this Olympics," the 27-year-old declared.
For Phelps, things can only get better after the man who swept eight golds at Beijing four years ago was forced into fourth position and missed out on a medal for the first time at the Games since he was a 15-year-old in Sydney in 2000.
The United States 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.
Britain was disappointed on Saturday when world champion Mark Cavendish was upstaged in the cycling road race by Kazakhstan's Alexandre Vinokourov, and on Sunday the hosts suffered another blow when women's marathon world record holder Paula Radcliffe withdrew from the Games because of injury.
The hosts' best next hope may be in the pool where Rebecca Adlington defends her 400 freestyle title, although she scraped into the final as the slowest qualifier. Adlington is up against Italian world champion and world record holder Federica Pellegrini and world number one Camille Muffat of France.
By late afternoon on Sunday, the United States were second in the medals table after Kimberly Rhode took the women's skeet shooting gold.
The Italians were in third place after the 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 on Saturday.
Day Two saw the latest incarnation of the U.S. basketball "Dream Team", this time featuring LeBron James, Kobe Bryant and Kevin Durant, begin their title defence with a comfortable 98-71 win over France after a joyful display of high-flying skill.
At Wimbledon, where rain forced the closure of the roof over centre court, women's second seed Agnieszka Radwanska crashed out in a surprise first-round defeat by world number 24 Julia Goerges of Germany while Britain's Andy Murray reached the second round by beating Switzerland's Stanislas Wawrinka.
On Saturday, Serena Williams breezed past Serbia's Jelena Jankovic in straight sets, with U.S. First Lady Michelle Obama cheering her on. (Additional reporting by Paul Casciato, Julian Linden, Kylie MacLellan and Patrick Johnston; Editing by Ken Ferris)