US swimmer Ryan Murphy set a new Olympic record to win gold in the men's 100m backstroke at the Rio Olympics on Monday.

Murphy posted a time of 51.97sec to eclipse the previous record of 52.16sec set by his countryman Matthew Grevers at the London 2012 Olympics.

China's Xu Jiayu took silver, 0.34sec behind Murphy, and David Plummer pocketed bronze, 0.43sec further back. Plummer is the oldest US Olympic debutant since 2004.

Australia's Mitchell Larkin was fourth in 52.43sec at the Olympic aquatics stadium.