Iga Swiatek had a reminder of the stellar rivalry that never was when she practised alongside Ash Barty on Saturday ahead of the Australian Open.

Australian Barty is the reigning women's singles champion at Melbourne Park, but she retired just weeks after lifting the trophy last year.

That shock decision from the then 25-year-old saw a figurehead of the WTA Tour make way, and Swiatek has taken her place as the undisputed world number one, saying Barty has inspired her to hit those heights.

The prospect of Barty and an ever-improving Swiatek fighting for the tour's biggest titles was dashed, and they only ever played twice, with Barty winning both times.

Barty announced on January 6 she is pregnant, and she appears to have no inclination to perform a retirement U-turn.

"For sure, when she retired, I felt like she still had the best tennis out there," Swiatek said after their light-hearted court session.

"So, I was pretty sad that I'm not going to be able to compete against her and maybe win.

"But on the other hand, she gave me a lot in terms of my motivation and my kind of willingness to practise even more and to have more variety on court.

"When I played against her, I felt like she just has all these different game styles and slice. Even in her book, she says she has five types of slice. I don't know how that's possible. I still haven't figured out only one type.

"I have huge respect for Ash. She really gave me huge motivation at the beginning of last season to get even better. I'm kind of grateful for that."

Swiatek will play the first night session match on Rod Laver Arena at this year's championships, taking on a familiar foe in Germany's Jule Niemeier.

At the US Open last September, the heavy-hitting Niemeier led by a set and a break against Swiatek in the fourth round, only to let the Pole back in and eventually surrender the third set 6-0. Swiatek went on to win the title, her third grand slam trophy success.

Niemeier also reached the Wimbledon quarter-finals, and Swiatek is wary of the opening test that awaits.

"We played at the US Open, and you saw how intense that match was, how tough," Swiatek said. "It's not going to be easy.

"But on the other hand, any match in a grand slam is always more intense and more stressful than other tournaments. I'll be ready for it.

"It's nice also that we played not so long ago, so I can take a lot from that match. Now I know how her ball feels on the racket. So, we'll see. But she has the same."