In one of the most stunning upsets in Olympic swimming history, Tunisia's Ahmed Hafnaoui became the lowest-seeded swimmer to win gold since 2004, when Kirsty Coventry won the 200 backstroke as the 21st seed.

Swimming alongside Hafnaoui, the U.S.' Kieran Smith unleashed the second fastest closing split in the field to win the nation's first medal in this event since Peter Vanderkaay in 2012.

While Austria's Felix Auboeck was third at the final turn, he narrowly missed the podium to place fourth in a tie with Germany Henning Mühlleitner who was the fastest finisher in the field.

The only swimmer in the field to dip under the 3:43 barrier, Australia's pre-race favourite Elijah Winnington (3:45.20) shot out to an early lead before starting to fade at the halfway mark and eventually come seventh.

Up to one swimmer per NOC meeting that time is eligible for selection, allocated by world ranking until the maximum quota for all swimming events is reached.