Hannah Miley's hopes of winning Great Britain's first medal of the 2012 Olympics were dashed when she finished fifth in a 400 metres individual medley race.
The gold medal was instead won by 16-year-old Ye Shiwen, who also set a new world record.
Ye, who won the 200m individual medley aged 15 at the World Championships in Shanghai last year, produced a superb freestyle to stretch away and touch in four minutes 28.43 seconds.
World champion Elizabeth Beisel was second with Ye's compatriot Xuanxu Li third.
For Miley, it was a disappointment as the 22-year-old had been strongly fancied to make it on to the podium after her breakthrough on the global stage last year when she was second in the World Championships in Shanghai.
Despite her best efforts, she touched two places outside the medals in 4mins 34.17secs.