In the second round, No.1 seed Simona Halep resumes her 2014 rivalry with Eugenie Bouchard. Both players broke into the Top 10 that year, with Halep ascending from No.11 to No.3 and Bouchard rising from No.32 to No.7, and played three times - with the Romanian taking their matches in Indian Wells and the WTA Finals, and the Canadian winning their Wimbledon semifinal. Since then, their careers have diverged. Halep has been the WTA World No.1 since October, while Bouchard is ranked No.112 - having fallen out of the Top 100 for the first time since April 2013 this week.
No.9 seed Johanna Konta and Eugenie Bouchard are the only two players remaining in the top quarter of the draw who have previously reached an Australian Open semifinal. Simona Halep has reached two quarterfinals, while Andrea Petkovic, Lucie Safarova and Karolina Pliskova have each made one quarterfinal in Melbourne.
No.21 seed Angelique Kerber will seek to extend her 10-match winning streak against Donna Vekic, whom the German defeated, 6-4, 7-6(5) in their only meeting to date, in the second round of Toronto last year. Vekic is now coached by Torben Beltz - Kerber's old coach.
Brisbane finalist Aliaksandra Sasnovich will bid to break her second round duck against No.28 seed Mirjana Lucic-Baroni. The Belarusian No.1 is 0-6 at this stage of Slams in her career so far - the only active player with a worse record is Urszula Radwanska, who is 0-9 in Slam second rounds. Sasnovich is also 0-2 against last year's semifinalist, although their first encounter in Toronto in 2015 had to be decided by a third set tiebreak.
No.14 seed Anastasija Sevastova will resume a rivalry with 2008 champion Maria Sharapova that gave fans two of the most epic matches of 2017. Sevastova vanquished the Russian in the fourth round of the US Open, winning 5-7, 6-4 6-2, but Sharapova gained her revenge in the first round of Beijing four weeks later 7-6(3), 5-7, 7-6(7).
No.20 seed Barbora Strycova trails her second-round opponent Lara Arruabarrena 1-2 in the head-to-head. The Spaniard's wins came on the indoor hard courts of Paris in 2014 and the clay of Madrid in 2017, while Strycova's only victory was in Fed Cup play at home last year. Arruabarrena, in a Slam second round for the sixth time (and first since Wimbledon 2015), has never made the third round of a major.
Lauren Davis is bidding to reach the third round of the Australian Open for the third time, and owns a 2-0 head-to-head lead over Andrea Petkovic. The American had a rollercoaster 2017, putting together a 17-9 record in WTA main draws through Rome in May - but going just 3-13 from then until the end of the year.
No.8 seed Caroline Garcia will notch up her 150th WTA victory if she wins her second round. Standing between the Frenchwoman and this milestone is 18-year-old Marketa Vondrousova, the youngest player in the Top 100 and the second youngest in the second round here.
No.18 seed and Sydney runner-up Ashleigh Barty clashes with Sydney semifinalist Camila Giorgi today. The home favorite leads the head-to-head 2-0 - one straight-sets win and one via retirement - but they have never played on hard courts.
The Ukrainian squad continue their charge: having sealed a national record of four women in the second round of a Slam on Tuesday, Lesia Tsurenko takes on No.26 seed Agnieszka Radwanska to make it four out of four in the third round, after victories on Wednesday for Elina Svitolina, Marta Kostyuk and Kateryna Bondarenko.
15-year-old phenom Marta Kostyuk is taking Melbourne by storm - last year's junior champion has become the youngest player since Martina Hingis in 1996 to reach the third round of a Slam. Find out more about Kostyuk's perfectionism and relationship to the sport in our WTA Insider interview with her.
Last year, Kostyuk became the first 14-year-old to win a junior Slam since Laura Robson at Wimbledon in 2008. Injuries set the Briton's career on a downward path - but she's in Melbourne for the doubles event, and talked to Kevin Mitchell for the Guardian about her recent life-changing experiences and future goals.
ORDER OF PLAY
Find out when and where players are up on the fourth day in Melbourne.
One of the most alarming moments of Simona Halep's first-round win over Destanee Aiava was when the No.1 seed went over on her ankle early in the second set. Afterwards, the Romanian updated the press on the status of her injury.