Both had already achieved the automatic 20 kilometre qualifying time for the Olympics so earned automatic nominations for the Games by being the first Australians to finish.

Bird-Smith, who won Olympic bronze at Rio 2016, clocked 1 hour 20min 52sec in February of last year to dip below the required men's time of 1:21.00.

He was third on the day in Adelaide, finishing in 1:23.01 behind Sweden's winner Perseus Karlstrom who came home in 1:21.57.

Canada's Evan Dunfee finished second in 1:22.32.

"Getting the automatic nomination was the game plan today, so I just got out there and tried to stick with an even pace, off a kind of curbed training block – so I'm just happy to be able to get the job done and focus on the remainder of the year now," said Bird-Smith, the Commonwealth Games gold medallist at Gold Coast 2018.

Montag won the women's race in 1:33.15 to make sure of her Tokyo 2020 place.

She also went under the required women's time of 1:31.00 in February 2019, clocking 1:30.51.

It was an Australian 1-2-3 as Katie Hayward was second in 1:34.00 and Beki Smith third in 1:35.06.

"It's a surreal feeling, a big childhood dream come true, my first Olympics, so a brilliant early birthday present and a huge relief," said Montag, the Commonwealth Games champion who is 22 on February 15.

"It was warm, much warmer than expected, but today was more about the position for me rather than time, so the pace was very, very conservative.

"It was all really a mental challenge but towards the end I saw my moment and tried to kick home."

Race walking at Tokyo 2020 will take place in Sapporo, more than 800 kilometres to the north of the capital because of concerns about high temperatures.