MELBOURNE, Australia -- Sofia Kenin knew this would be a tough test at the Australian Open, a potentially early end to her first attempt to defend a Grand Slam title.
Upon realizing she probably would be playing big-hitting veteran Kaia Kanepi in the second round, Kenin acknowledged, she "maybe kind of broke down a little bit."
Kenin was right to be worried. And, with Kanepi at her best, this one was over quickly. Delivering 10 aces, Kanepi powered her way past the No. 4-seeded Kenin, overwhelming the 2020 champion 6-3, 6-2 in just 64 minutes on Thursday.
"I obviously felt like I'm not there 100% -- physically, mentally, my game. Everything just feels real off, obviously. It's not good," Kenin said at her news conference, where she wiped away tears.
"I mean, I just -- I know I couldn't really handle the pressure," she said.
There's very little that's subtle about Kanepi's game, and there wasn't much nuance in the way she described her approach to this match: "I served really well today. I think this helped a lot. My game plan was to play aggressive, as I normally do."
That pretty much sums it up.
This was certainly a significant upset based on rankings: Kanepi, an Estonian, is currently 65th. And based on past accomplishments: In addition to her title at Melbourne Park, Kenin reached the French Open final last year, while Kanepi is 0-6 in Grand Slam quarterfinals.
But the result did make some sense.
After all, Kanepi, 35, had beaten Kenin, 22, in their only previous matchup, part of why this was not a contest the American was looking forward to. Plus, Kanepi has been successful against some of the best on the biggest stages, with seven victories over top-10 opponents at Grand Slam tournaments, including against then-No. 1 Simona Halep at the 2018 US Open.
And then there was recent form.
Kenin walked off the court crying after a 6-2, 6-2 loss last week in a tuneup event at the site of the Australian Open and explained afterward that her left leg was sore. Kanepi, meanwhile, put an end to No. 7-ranked Aryna Sabalenka's 15-match winning streak last week and entered Thursday having won 16 of her past 17 outings.
With serves topping 110 mph, Kanepi saved all seven break points she faced. And she wound up with a 22-10 edge in winners.
"I couldn't find my rhythm," Kenin said. "I was obviously way too nervous."
Her departure meant three of the top nine seeded women already were gone before midway through Day 4 at a Grand Slam tournament where routines have been disrupted by the pandemic, joining No. 8 Bianca Andreescu (the 2019 US Open champion) and No. 9 Petra Kvitova (a two-time Wimbledon winner) on the sidelines.
Serena Williams remains the last woman to successfully defend a Grand Slam title -- at Wimbledon way back in 2016.
Top-ranked Ash Barty did manage to avoid a surprise Thursday, but she blew a big lead in the second set and survived a shaky tiebreaker to get past Daria Gavrilova 6-1, 7-6 (7).
Barty is trying to become the first Australian to win the women's title at Melbourne since Chris O'Neil in 1978.
"It's a different challenge every single day," Barty said. "It's trying to be the best I can every single day, whatever that level is."
Other winners included No. 5 Elina Svitolina, American Shelby Rogers and former No. 1 Karolina Pliskova.
Barty lost only 10 points in the opening round, and her match against Gavrilova was equally lopsided until the wobbly finish. She led 5-2 in the second set but was broken twice serving for the victory.
In the tiebreaker Barty lost several ugly points. Gavrilova, a wild card, failed to convert two set points and committed unforced errors to end the final three rallies.
The two friends then shared a hug at the net.
"When you play another Aussie, rankings go out the window, experience goes out the window," Barty said. "Typically you know each other so well. It's always going to be a tricky match."
Svitolina beat 16-year-old Coco Gauff 6-4, 6-3. She has reached the quarterfinals in Australia twice and showed her experience as she took on Gauff for the first time. She made the most of her only break-point chance in the second set to take a 5-3 lead and then served it out.
Svitolina will play No. 26-seeded Yulia Putintseva in the third round.
Gauff was the youngest player in the women's draw. She was unable to repeat her performances from her breakout major in Melbourne last year. She reached the round of 16 at the 2020 Australian Open with wins over Venus Williams and Naomi Osaka before losing to eventual champion Kenin.
Rogers reached the third round at the Australian Open for the first time by beating Olga Danilovic 6-2, 6-3. Rogers, 28, came into the tournament with a career record of 1-4 in Melbourne, but her ranking and fortunes have been on the rise of late.
She reached the quarterfinals at the US Open for the first time last September, and her year-end ranking was a career-best No. 58. Rogers was sidelined for 14 months by a knee injury sustained in early 2018, and her ranking at the end of that year was 780th.
She had little trouble with Danilovic, a qualifier from Serbia ranked 183rd. The small crowd on Court 3 included Novak Djokovic, who sat behind the baseline shouting encouragement to his fellow Serb.
Pliskova, seeded sixth, advanced by beating American Danielle Collins 7-5, 6-2. Pliskova lost serve twice in a seesaw first set but pulled it out and then pulled away to beat Collins, a 2019 semifinalist at Melbourne Park.
In an all-American match, No. 22 Jennifer Brady beat Madison Brengle 6-1, 6-2.
The Associated Press contributed to this report.