Olympic champion Park Tae-hwan was reinstated for the 400-meter freestyle event Saturday after South Korea appealed his disqualification for a false start on the opening day of the swimming competition.
FINA executive director Cornel Marculescu told The Associated Press that the sport's governing body made the decision after reviewing video.
Park finished fourth in 3 minutes, 46.68 seconds. The reversal of the disqualification knocks out Ryan Cochrane of Canada, who had taken the last qualifying position for Saturday's night final in eighth.
The protest first went to FINA's technical swimming committee, which upheld the disqualification. South Korea then took it to a jury of appeal, which ruled in Park's favor.
Canada cannot appeal because the jury's decisions are final.
Park was first to touch the wall in his heat and appeared bewildered when told of the disqualification.
''I don't know why,'' said Park, who won gold in the event at the Beijing Games. ''I need to speak to my coach to find out.''
Marculescu could not explain why the judge on the pool deck called for a disqualification.
''It's a very good question,'' Marculescu said. ''Human error maybe.''