Ana Ivanovic exited the Australian Open following a dramatic encounter with Madison Keys that was disrupted by the collapse of the Serbian's coach Nigel Sears, while Garbine Muguruza suffered a shock third-round defeat on Saturday.
Ivanovic (20) was leading 6-4 1-0 before the match was delayed by almost an hour after Sears - father-in-law to Andy Murray - collapsed in the stands at Rod Laver Arena.
Sears was later reported to be conscious and responsive, but Ivanovic struggled for consistency upon resumption and saw her hopes in Melbourne come to an end for another year as 15th seed Keys progressed 4-6 6-4 6-4.
Wimbledon finalist Muguruza had coasted through the first two rounds, but the third seed was out of sorts in a 6-3 6-2 defeat against Barbora Strycova.
However, Victoria Azarenka (14) continued to show why she is considered as one of the biggest threats to defending champion Serena Williams in a dazzling 6-1 6-1 beating of Naomi Osaka.
Ivanovic had led 4-2 in the second set and 3-0 in the decider, but Keys - a semi-finalist in Melbourne 12 months ago - showed her quality at the crucial moments to book a spot in round four.
Strycova upset the odds to reach the round of 16 at the Australian Open for the first time. The Czech had not taken a set off Muguruza in two previous meetings, but the Spaniard was outclassed under the Rod Laver roof.
Two-time winner Azarenka lost her first service game against Osaka, only to emphatically reel off the next eight. The Belarusian was on court for less than an hour and she has now dropped just five games in three matches.
Johanna Konta, who beat Venus Williams in round one, also reached progressed. The Australia-born Briton comfortably defeated Denisa Allertova 6-2 6-2.
Qualifier Shuai Zhang had already accounted for Simona Halep (2) and Alize Cornet in Melbourne, and the world number 133 continued her dream run with a 6-1 6-3 victory over Varvara Lepchenko.
SEEDS SAYING GOODBYE
As well as Muguruza and Ivanovic, Karolina Pliskova (9) suffered a surprise of sorts in a 6-3 6-2 loss to Ekaterina Makarova on Margaret Court Arena.
Makarova, seeded 21st, has a decent record in Melbourne, having reached the quarter-finals in 2012 and 2013, as well as the semi-finals last year.
Konta's victory means she is the first Briton to reach the Australian Open fourth round since 1987.
Muguruza won just 27 of 70 points from the baseline during her 76-minute loss to Strycova.
Keys' performance was somewhat erratic against Ivanovic. The American hit 44 winners, but also recorded 52 unforced errors.
SOCIAL MEDIA SWEEP
"Thank you for all your nice tweets and words of encouragement. The crowd was amazing tonight! So grateful for all my fans around the word!" - A grateful Ivanovic thanks her supporters on Twitter after an emotional day on court.
"Practice makes perfect..." Azarenka wasted little time celebrating her dominant victory. The Belarusian posted a video of her hitting on the practice courts following her win against Osaka.
THEY SAID WHAT?
"Clearly not my best day, for sure. I think today is a very bad day at the office. I think Barbora played good, very good. Also, I didn't play good." - Muguruza laments an off-day in Melbourne.
"I just try to focus on my execution more. The score doesn't really say pretty much the whole story sometimes." - In-form Azarenka insists she has further room for improvement.
"It just feels like I'm competing to the best of my ability and that's all I can ask for." - Konta revels in her excellent run at the Australian Open.
Strycova will have to upset the odds again to reach the quarter-finals as she comes up against Azarenka in round four.
Konta can make a grand slam quarter-final for the first time, but must overcome a potentially tough contest versus Makarova first.
Angelique Kerber comfortably saw off Madison Brengle in straight sets and next faces an all-German encounter with Annika Beck.
World number one Serena Williams returns to action on Sunday in a fourth-round contest against Margarita Gasparyan. Maria Sharapova (5) faces the tricky Belinda Bencic (12), and Agnieszka Radwanska (4) is up against Anna-Lena Friedsam.
Barbora Strycova beat Garbine Muguruza (3) 6-3 6-2
Angelique Kerber (7) beat Madison Brengle 6-1 6-3
Ekaterina Makarova (21) beat Karolina Pliskova (9) 6-3 6-2
Victoria Azarenka (14) beat Naomi Osaka 6-1 6-1
Madison Keys (15) beat Ana Ivanovic (20) 4-6 6-4 6-4
Johanna Konta beat Denisa Allertova 6-2 6-2
Annika Beck beat Laura Siegemund 6-0 6-4
Shuai Zhang beat Varvara Lepchenko 6-1 6-3