Michael Phelps won the 19th Olympic gold medal of his career on Sunday after helping the U.S. men's team to victory in the 4x100 metres freestyle relay.
The 31-year-old, making his first competitive appearance at his fifth Games after sitting out the heats, now has 23 medals, with two silvers and two bronzes filling out his tally.
London 2012 champions France took the silver medal and Australia the bronze.
The most decorated Olympian of all time has now won gold at four separate Games, the first swimmer to do so.
The victory maintained a run of U.S. success in the event, with the Americans medalling in every 4x100 freestyle relay raced at the Games since it was first included in 1964.