Sofia Kenin's title defence came to a shock end in the second round of the Australian Open, where world number one Ash Barty advanced amid injury concerns.
Kenin was looking to become the first woman to defend her crown at Melbourne Park since Victoria Azarenka in 2013, instead, she was a high-profile casualty in warm conditions on Thursday.
Barty, who lost to Kenin in last year's semi-finals in Melbourne, stayed alive with a straight-sets win over fellow Australian Daria Gavrilova.
Former world number one Karolina Pliskova also progressed beyond the second round as fifth seed Elina Svitolina blitzed American sensation Coco Gauff.
KENIN OUSTED IN BOILOVER
The American star arrived at the year's first grand slam with high expectations and looking to become the first woman to go back-to-back at a major since Serena Williams in 2016.
But fourth seed Kenin fell to experienced Estonian Kaia Kanepi 6-3 6-2, having tallied 10 winners and 22 unforced errors in windy conditions in Melbourne - the scene of her breakthrough slam more than 12 months ago.
It was Kenin's first defeat to a player ranked outside the top 50 since going down to then-number 54 Iga Swiatek in the 2020 French Open final.
Asked why she was nervous pre-match, Kenin told reporters: "It's like the outside pressure. I felt really nervous. I haven't felt my game for, I don't know how long, but I haven't really felt my game so well, even in my first round.
"I played well, but still haven't felt 100 per cent game-wise. It's obviously tough."
STRAPPED THIGH? NO WORRIES FOR BARTY
Barty's left thigh was heavily strapped amid concerns but the 2019 French Open champion still booked her spot in the third round with a 6-1 7-6 (9-7) win over countrywoman Gavrilova.
The first Australian woman to reach the semi-finals in Melbourne since 1984, following last year's run, Barty gave up a 5-2 lead in the second set before saving two set points in the tie-break.
Reflecting on Kenin's surprise exit, Barty talked up the standard of the WTA Tour.
"There are no easy matches," said Barty, who next meets 29th seed Ekaterina Alexandrova for a spot in the round of 16. "There are no easy matches in any tour event, any slam, anything. I think every time you walk on the court, you have to try and be able to bring your best tennis to be able to compete with everyone.
"That's just the level that there is now on the women's side. That's something really exciting about women's tennis now, is that every single match, it's a fair match. You go out there, you play hard, you try to do the best that you can."
PLISKOVA AVENGES LOSS, SVITOLINA TOO GOOD FOR GAUFF
Beaten by Danielle Collins in the third round of the Yarra Valley Classic just eight days ago, sixth seed Pliskova got the better of the 2019 Australian Open semi-finalist this time around.
Pliskova - also a semi-finalist at Melbourne Park two years ago - defeated Collins 7-5 6-2 and next plays 25th seed Karolina Muchova.
"I just played better in some moments, which I didn't last week. Then she was not playing that well as she did last week," Czech star Pliskova said. "I knew if I at least maintain little bit, just play at least similar as I was playing last week, I knew it's going to be difficult for her to repeat what she played last week. I think she really played great."
Owning a 6-1 record in the second round at Melbourne Park - falling only at this stage in 2016 - Svitolina produced a mature performance to conquer 16-year-old star Gauff 6-4 6-3 on centre court as 26th seed Yulia Putintseva awaits.
Elsewhere, seeds Belinda Bencic, Elise Mertens, Anett Kontaveit, Jennifer Brady and Donna Vekic moved through.