Current women's world No.1 Ashleigh Barty heads the Australian contingent as the action and weather heats up at Melbourne Park.

After rain and mild temperatures so far, the mercury is expected to tip 30 degrees on Wednesday before showers and another cool change.

Barty will be hoping to heat up a bit earlier in her match against Polona Hercog, the Queenslander a little sluggish in dropping the first set in her opener against Lesia Tsurenko.

Yet she remains comfortable in digging herself out of holes.

"Knowing that I've come back from being a set down in many matches is good. I'd prefer not to be in that situation," she said.

"It's good knowing I have the ability to trust myself when I need to."

Recent nemesis Petra Kvitova precedes the match, kicking off the day's action on Rod Laver Arena with a second round encounter against Paula Badosa.

Serena Williams will be a warm favourite when she takes on Tamara Zidansek, Naomi Osaka is expected to keep her title defence in check with a win over Saisai Zheng while Caroline Wozniacki rounds out the roll call of former women's No.1s when she plays Dayana Yamstremska.

Elsewhere, two of the 'big three' play second round matches.

Roger Federer gets the late late show after Williams' match on Rod Laver Arena, when he faces off with Filip Krajinovic.

Pulling out of the ATP Cup to spend time with family and not playing a lead-up tournament in Australia, Federer knows he has to quickly build into the tournament.

"I just haven't played proper matches in many, many weeks, and a lot of guys, probably 95 per cent of the guys are coming here with matches," he said.

"So I think for me really the first three rounds are key to get going, to get used to the pressure, stay calm ..."

After losing a set in his opening round encounter with Jan-Lennard Struff, Novak Djokovic will be hoping for a more leisurely afternoon when he plays world No.146 Tatsuma Ito.

Australian Astra Sharma has the rare distinction of playing an opening round match on day three when she goes up against 28th seed Anett Kontaveit, rain on day one blowing out the schedule.

Compatriots Jordan Thompson, John Millman and first round five-set here Marc Polmans also feature.

Australian Associated Press