The women's Australian Open draw was shaken up by second-round defeats for Garbine Muguruza, Anett Kontaveit and Emma Raducanu at Melbourne Park.
The first three days saw very few upsets but Thursday began with a bang as third seed Muguruza lost 6-3 6-3 to French veteran Alize Cornet while sixth seed Kontaveit was toppled 6-2 6-4 by Danish teenager Clara Tauson.
Both were among the title favourites having finished last season very strongly.
Muguruza, the beaten finalist here two years ago, won the WTA Finals in November but her preparation for the new season was disrupted when all her coaching team contracted Covid-19.
"It's a tough day," said the Spaniard. "I didn't feel at all my game. My serve wasn't there. I think my shots weren't there also. Tactically I think I wasn't doing the right decisions either. On top of that she played very well, very solid game. I think she plays better when she's playing against top players."
Cornet, 31, has pulled off a number of upsets in her career and reached the fourth round at all of the slams.
She said: "I think today the key was that I'm telling myself that I'm playing probably my last year. I'm not sure yet. When I stepped on the court, I was like, 'You know what, just enjoy the moment because you don't know if you're going to come back'."
Tauson is at the other end of her career and is making her main draw debut in Melbourne having won the junior title three years ago.
The 19-year-old is already a top-40 player and was superb on Margaret Court Arena against a player in Kontaveit who surged into the top 10 at the end of last season.
"Today we had a plan that I didn't really follow because I felt really good out there, so I went for everything in my shots," said Tauson.
"It's the first time I'm in the third round of a slam. Playing a player like her to reach it, it's a really big achievement for me. Obviously it was one of the things I really wanted to do, to beat the good players in the bigger tournaments."
History maker 🇲🇪@DankaKovinic upsets Emma Raducanu 6-4 4-6 6-3 to become the first player representing Montenegro to reach the third round of a Grand Slam.
— #AusOpen (@AustralianOpen) January 20, 2022
🎥: @wwos @espn @Eurosport @wowowtennis #AusOpen #AO2022 pic.twitter.com/wauKCPG1KU
Raducanu was proud of her fighting spirit after revealing she might not even have taken to the court for her second-round encounter.
The US Open champion was beaten 6-4 4-6 6-3 by Montenegro's Danka Kovinic in a bizarre match that saw her reduced to hitting slice forehands because of a painful blister on her right hand.
Raducanu took a medical time-out for treatment after only five games and was hampered throughout but somehow won the second set before going down in three.
"It was a difficult match," said the 19-year-old. "I was struggling with my hand before the match. There were some people in my team that maybe didn’t want me to play but I wanted to go out there and fight through it, see how far I could get."
Raducanu was forced off court for three weeks last month after contracting Covid-19, and she said: "I have been struggling with blisters since I started playing really in Australia because 21 days, no tennis, my hands got pretty soft.
"From day one, day two, I was getting blisters pop up here and there. This particular one has been with me for about five days and I have been trying to tape it for every practice, and it would harden and dry out, but then once I would play again, another layer would just keep ripping off.
"It ended up being pretty deep. It’s a bit annoying because I know it’s something that will heal in a few days, but it’s just unfortunate timing."
This was another new situation for Raducanu, who was the big favourite for a grand slam match for the first time against the world number 98, but she looked calm initially, rattling through the first three games.
It soon became clear all was not well, though, and Kovinic won five games in a row either side of a lengthy medical time-out for Raducanu.
By the start of the second set, the 19-year-old was hitting almost exclusively slice forehands – a rarely-used shot in the professional game – but it unsettled Kovinic.
Despite her inexperience, competitive nous is clearly one of Raducanu’s big strengths and she managed to take the second set, smiling and laughing at the absurdity of it all.
A sharp wince while she received more treatment ahead of the third set showed just what Raducanu was dealing with and, although she managed to hit through her forehand a little more in the deciding set, it was not enough.
Sabalenka survives 💪
— #AusOpen (@AustralianOpen) January 20, 2022
No.2 seed @SabalenkaA digs deep for a 1-6 6-4 6-2 comeback win over Xinyu Wang.#AusOpen · #AO2022
🎥: @wwos · @espn · @eurosport · @wowowtennis pic.twitter.com/xo6uklNhNq
Aryna Sabalenka lost her opening two matches of the season amid a plethora of double faults and, four matches into 2022, her tally now stands at 70.
She sent down 19 against China's Wang Xinyu on Thursday, including six in the opening game, but came from a set down to claim a 1-6 6-4 6-2 victory.
Seventh seed Iga Swiatek has had a much easier time of things so far and she eased to a 6-2 6-2 victory over Rebecca Peterson but it was the end of the road in singles for Australian veteran Sam Stosur, who was beaten 6-2 6-2 by 10th seed Anastasia Pavlyuchenkova.
Stosur, the 2011 US Open champion, will only play doubles after this tournament.