Ons Jabeur suffered a shock second-round exit at the Australian Open on Thursday, becoming the latest seed to fall at Melbourne Park.
The Tunisian number two seed was beaten 6-1, 5-7, 6-1 in 1hr 41min by Czech world number 86 Marketa Vondrousova.
"I think she just got better, you know, in the second set," Vondrousova said.
"She played some amazing points. I just tried to stay focused and play my game. And I'm just so happy to be through."
Vondrousova, 23, was ranked as high as 14th in 2019 and is on the comeback trail after an injury-hit season which resulted in surgery on her left wrist.
"It's always tough to come back after such a long time," she said.
"I just started in November and I felt good and I did great," said the left-handed Vondrousova, who reached the last 16 at Melbourne Park in 2021.
"I worked on my fitness a lot and I'm just very happy to be back on this level and to be able to play these sorts of matches."
Jabeur had only fleetingly showed the form that took her to two Grand Slam finals during a shaky opening-round win.
The Tunisian eventually saw off 98th-ranked Tamara Zidansek 7-6 (10/8), 4-6, 6-1 after 2hr 17min in an unconvincing display littered with unforced errors.
And in a late-night match that did not start until 11.24 pm on Rod Laver Arena, she struggled again.
Jabeur dropped her first service game against Vondrousova, who raced into a 3-0 lead.
Vondrousova had lost all three of her previous tour-level matches against Jabeur but this was their first meeting on a hard court.
The Czech broke again for 5-1 and secured the set in just 24 minutes of dominant tennis.
Jabeur, who missed last year's Australian Open with a back injury, won Madrid and Berlin trophies last year in a breakout season which propelled her to second in the rankings.
She hit back at the start of the second set but was broken again when serving for the set at 5-3.
Jabeur then blew a set point on Vondrousova's next service game, but at 6-5 created another chance and this time converted.
It was a rare moment to celebrate in a desperate performance devoid of any spark against an inspired opponent who simply made fewer errors.
Vondrousova was not to be denied, quickly securing a triple break in the final set for a famous win.
It puts her into an all-Czech third-round clash against Linda Fruhvirtova, the world number 82.