Electric Aussie swimmers McKeown, McKeon set 2021 pace in Sydney

Australia's Kaylee McKeown swam the fourth fastest 200m backstroke time ever

Kaylee McKeown clocked the fourth quickest women's 200 metre backstroke time ever Friday while Emma McKeon swam the year's fastest 100m freestyle as the Australian pair stepped up preparations for the Tokyo Olympics.

McKeown, 19, smashed her own Commonwealth and Australian record by touching in 2min 04.31sec at the Sydney Open, the number one time in the world over the last 18 months.

It was a warning shot to American world record holder Regan Smith, who owns the best time in history (2:03.35) set in 2019.

Smith also holds the second quickest ahead of 2012 Olympic champion Missy Franklin, with McKeown now claiming fourth and fifth.

"I just trusted myself a bit more in the first 100m today to get out a little faster which did hurt a lot in the back-end but I did a really good solid time, so I'm happy with that," she told reporters.

"It's always our plan to put as much pressure on as we can at these meets to get the most race practice we can."

Australia's Olympic trials are in Adelaide next month, with McKeown's key challenger, triple Olympian Emily Seebohm, touching second Friday in 2:07.06.

McKeon, part of Australia's gold-medal-winning 4x100m relay team at the 2016 Rio Olympics, was also on fire, upsetting sprint star Cate Campbell to take the women's 100m.

Her 52.29 was a world-best for 2021 and put her in the top six fastest ever, led by Swedish world record holder Sarah Sjostrom's 51.71.

"It gives me confidence racing the mornings and I've just got a lot stronger and done a lot of work in the gym. That's where I think I've made big gains," said McKeon.

"And every time I get to race Cate and be up against the best in the world it adds to my confidence and it's just good race practice."

The finals in Sydney are being swum in the morning, mimicking the schedule in Japan, where heats will also be in the evening.