McKeown's victory in Saturday's final, where compatriot Emily Seebohm won bronze, follows her 100m backstroke win.

The 20-year-old's triumph gives Australia a 10th gold medal of the Tokyo Games.

And the victory puts the swim team, with seven golds, on the cusp of equalling Australia's most successful Olympics at the pool, the eight golds won in the 1956 Melbourne Games.

In the medal race, McKeown lurked behind Canadian Kyle Masse for the initial three laps.

McKeown was 0.80 seconds behind at the halfway stage and then turned for the last lap 0.69 seconds shy of Masse.

But the Australian timed her surge to perfection, reeling in Masse over the final 15 metres to become the seventh woman to complete the 100m-200m backstroke gold double at an Olympics.

McKeown won in two minutes 04.68 seconds from Masse (2:05.42) .

And Seebohm, at her fourth Olympics, clocked 2:06.17 to add a cherished bronze to her two silver career medals.

Australian Associated Press