McKeon stood shoulder-to-shoulder with the great Cate Campbell at the blocks, but 100 metres later was an arm's length clear, clocking 52.49 seconds, the third fastest freestyle time in the world this year.

It's an important stepping stone on her way to the trials in June - and barring another COVID-19 shutdown - a second Olympics in Tokyo.

McKeon had stood down from the 200m freestyle final, despite being the fastest qualifier, to manage her workload and the move paid off.

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The finals had been moved to the morning session to allow the Australian athletes to adjust to the schedule in Tokyo, largely designed to cater for the US television audience when the Games begin in late July.

It hasn't proved an obstacle for the Wollongong product, who turns 27 next month.

"It is physically a little bit harder I think getting up in the morning, but actually I don't really find it that hard," McKeon said.

"We train early in the morning and this is four hours after I usually train.

"It's more of a mental state as well. Just knowing it's a final.

"Once we get to an Olympics, it's an Olympic finals so no matter what time of day it's on, you're going to be ready to go. In Rio we were swimming at midnight or something, we'll be ready no matter what."

After winning her semi-final, Campbell had finished sixth in the 100m at Rio de Janeiro in 53.24s, behind sister Bronte who was fourth.

McKeon did not compete in the event but finished the Olympics with one gold and two silver relay medals.

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But her finest effort came in the 200m freestyle final, where she claimed bronze behind Katie Ledecky and Sarah Sjostrom.

Now almost five years on, with Tokyo 2020 delayed until this year because of the worldwide pandemic, changes to McKeon's training regime is paying dividends over the shorter distance.

"I pulled out of the 200 just to make sure I can get some good weeks of training after this leading into the next couple of meets and then trials," McKeon said on pool deck after winning the 100m.

"I was happy with that kind of time, [competing] in the morning.

"I've been doing a lot of work on my kick, so when they're burning I know that I've done that kind of work, knowing they're not going to slow down."

Campbell experienced morning finals at the 2008 Beijing Games and said while she suffered somewhat from her fast swim the night before, she was happy with her form heading towards June's Olympic trials. with AAP