Eight of the 16 women remaining are Grand Slam champions - four in each half - with a further two former major finalists. For the second consecutive major, 13 of the last 16 spots have been taken by seeded players.
All four of today's fourth-round clashes are repeats of match-ups that have taken place on the WTA Tour in the past year. The most stunning of those was Amanda Anisimova's 6-2, 6-4 upset of Petra Kvitova in the third round of Indian Wells last year - a loss that snapped a 14-match winning streak for the Czech. Anisimova, who was 16 years old at the time, became the youngest player to record a Top 10 win since a 16-year-old Nicole Vaidisova's defeat of Nadia Petrova in the 2005 Bangkok final, and she remains the youngest current player to hold a Top 10 win.
No.5 seed Sloane Stephens is unbeaten against Anastasia Pavlyuchenkova in two previous meetings: a straightforward 6-1, 6-2 win in the 2015 Washington final and a rather more dramatic 6-7(8), 6-4, 6-4 marathon in the first round of Beijing three months ago. The Russian will be bidding for the 30th Top 10 win and 13th Top 5 win of her career - though only one of the latter has come on the Grand Slam stage, her upset of World No.3 Vera Zvonareva at Roland Garros 2011.
Maria Sharapova leads the head-to-head against Ashleigh Barty 1-0, having beaten the Australian 7-5, 3-6, 6-2 in the first round of Rome last year. Sharapova is bidding for her first quarterfinal in Melbourne since 2016, while Barty is aiming to become the third home player this millennium to reach the last eight here, following Alicia Molik in 2005 and Jelena Dokic in 2009.
No.2 seed Angelique Kerber's only previous meeting with Danielle Collins was a quick win for the German, 6-1, 6-1 in the third round of Eastbourne last year. If Kerber wins, it will mark the first time in the 31-year-old's career that she has reached the second week at any of the Slams for four consecutive years. Collins is bidding for the second Top 10 win of her career following her defeat of Venus Williams in Miami last year.
17-year-old Amanda Anisimova is the youngest player to make the second week of a major since Tamira Paszek's run to the Wimbledon fourth round in 2007, in which the Austrian defeated Barbora Strycova, Tatiana Golovin and Elena Dementieva before losing to Svetlana Kuznetsova. Anisimova is the youngest player to reach this stage in Melbourne since a 16-year-old Nicole Vaidisova in 2006; the Czech beat Anna Chakvetadze and Flavia Pennetta before falling to Amélie Mauresmo.
Petra Kvitova is bidding for her first Grand Slam quarterfinal since the 2017 US Open - and first in Melbourne since 2012. Overall, the Czech is 10-6 in Slam fourth rounds.
Coming into this week, Danielle Collins had yet to win a match at a major in five previous appearances. The Australian Open was the only Slam main draw at which the American had yet to compete, though - and on her debut, she has progressed all the way to a second week breakthrough.
Anastasia Pavlyuchenkova has reached the fourth round of a Grand Slam on five occasions - and four times, once at each Slam, the Russian went on to make the quarterfinal. Her sole loss at the fourth-round stage came at the 2010 US Open, her second-week debut, to Francesca Schiavone. Sloane Stephens, by contrast, has a 5-6 losing record in this round of majors. A Pavlyuchenkova win would mark the 27-year-old's first multiple quarterfinal showing at a Slam, while a Stephens victory would mean that the American holds three major quarterfinals in a 12-month period for the first time.
Angelique Kerber is the only player left in the draw yet to drop serve - though with 10 games conceded she is second in that department to Serena Williams's nine. Ashleigh Barty, meanwhile, is the joint ace leader with Elina Svitolina on 24 so far.
University of Virginia alumna Danielle Collins is just the fourth collegiate player to reach the last 16 at a Grand Slam, following Lisa Raymond, Jill Craybas and Laura Granville. A win over Kerber would make the American the first collegiate major quarterfinalist since Raymond at the 2004 Australian Open.
Dayana Yastremska may have fallen to idol Serena Williams in the third round - but the 18-year-old Ukrainian still "turns it up to 11", writes Jeff Sackmann at Tennis Abstract, topping the "aggression score metric" for the entire Tour.
There are two players representing Russia in the last 16 of this year's Australian Open - but that's not the extent of the tennis powerhouse's impact on the tournament, with plenty more players connected in some way to Russia, points out Richard Evans at tennis.com.
Amidst drama elsewhere, home favorite Ashleigh Barty's success "writes the story Australian tennis badly needs right now", argues Kevin Mitchell for the Guardian.
Naomi Osaka distinguished herself by demonstrating "the calm of a champion" in her comeback win over Hsieh Su-Wei, writes Matt Zemek at Tennis With An Accent.
ORDER OF PLAY
Click here for Sunday's order of play at Flinders Park.