Top-ranked Iga Swiatek is out of the Australian Open after a 3-6, 6-3, 6-4 third-round loss to 50th-ranked Linda Noskova on Saturday.
Swiatek is a four-time major winner but has never been past the semifinals at Melbourne Park.
The 19-year-old Noskova is playing in the main draw of the Australian Open for the first time.
Swiatek beat 2020 Australian Open champion Sofia Kenin and 2022 finalist Danielle Collins in the first two rounds and was on an 18-match winning streak.
But, after taking the first set against her Czech opponent, she struggled for rhythm.
After saving a breakpoint in the seventh game of the second set, Noskova won 11 of the next 12 points to level the match at one set apiece.
Noskova continued to pound away and troubled Swiatek, who held at love in the penultimate game and made her rival serve it out.
After falling behind 0-30, Noskova won four points to finish it off quickly. She earned a match point with an ace and sealed it when Swiatek sent a forehand long.
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(With AP inputs)