While Canada's defending Bronze medallist Kylie Masse led at the halfway mark, she could not withstand McKeown's late charge, touching for silver in 57.72 - only 0.02 seconds off her national record.

U.S.' previous world record holder Regan Smith was unable to replicate her time from the heats and semi-finals, settling for bronze in 58.05.

Meanwhile, Great Britain's Kathleen Dawson could not repeat her stunning 58.01 swim from the European Championships months earlier, placing sixth.

Up to two swimmers per National Olympic Committee (NOC) could automatically qualify by swimming that time at an approved qualification event.

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