Michael Phelps secured gold in his last individual event before he is due to retire, winning the men's 100m butterfly.
The 27-year-old surged late on to secure the 21st Olympic medal of his career.
South Africa's Chad Le Clos and Evgeny Korotyshkin both touched the wall at the same time to tie for silver.
It was Phelps's third gold medal of London 2012, and takes his total at the Games to five.
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