By Alan Baldwin
RIO DE JANEIRO (Reuters) - South Korea's Park Tae-hwan, the 2008 Olympic champion who won a late battle to swim at the Rio Games after appealing against a doping ban, failed to qualify for the men's 400 meters freestyle finals on Saturday.
The 2012 silver medalist finished fourth in his heat, won by China's world and Olympic champion Sun Yang, but his time of three minutes 45.63 seconds left him 10th overall with only the top eight going through.
Sun, China's big hope, was fourth fastest overall in a line-up led by Conor Dwyer of the United States with a time of 3:43.42.
Dwyer was followed by Australia's Mack Horton in 3:43.84 and Italian Gabriele Detti.
Park, the first Korean to claim an Olympic swimming medal when he won the 400 freestyle in Beijing in 2008, completed an 18-month ban imposed by world governing body FINA in March after testing positive for testosterone ahead of the 2014 Asian Games.
Under a controversial Korean Olympic Committee regulation, he was then hit with an additional three-year ban from the national team the day the FINA suspension expired.
That would have ruled him out of contention for Rio but the Court of Arbitration for Sport cleared the 26-year-old to compete.
Park is also due to swim in the 100m, 200m and 1,500m freestyle races in what will be his fourth and final Olympics.
The 400m final is later on Saturday.
(Editing by Ed Osmond)