World number one Ash Barty firmed as favourite for the Australian Open title when she breezed past Camila Giorgi in the third round on Friday just as reigning champion Naomi Osaka was being dethroned by Amanda Anisimova.
Barty's potential fourth round matchup against Osaka had been the talk of Melbourne Park since the draw was made but Anisimova tore up the script with a stunning victory on Margaret Court Arena. Some half an hour earlier on the neighbouring Rod Laver Arena, Barty had completed a clinical 6-2 6-3 victory over Italian Giorgi to sweep into the second week of the championships.
Anisimova, ranked 60th in the world, saved two matchpoints and smashed winners at will to beat reigning champion Naomi Osaka 4-6 6-3 7-6 (10-5).
Anisimova produced a superb display to knock out the Japanese and disappoint those who had been salivating at the prospect of a fourth-round showdown between the four-times major winner and Australian world number one Ash Barty.
"I just want to soak in this moment," Anisimova told reporters. "I'm just extremely happy. It was an amazing match. It was very close. It sucks we couldn't both win today, because these matches are hard. Honestly, I think she's a very nice girl. These days are kind of tough."
Nadal repels Khachanov
Meanwhile, sixth seed Rafa Nadal dropped his first set at this year's Australian Open but still powered through to the fourth round with a 6-3 6-2 3-6 6-1 defeat of Karen Khachanov.
The Spaniard, seeking to claim a record 21st Grand Slam title in the absence of great rivals Roger Federer and Novak Djokovic, was sensational as he took a two-set lead.
But Khachanov, seeded 28th, threw caution to the wind in the third set, stalling Nadal's charge with some ferocious hitting. Olympic runner-up Khachanov had lost all seven previous meetings with 2009 Australian Open champion Nadal but briefly looked capable of mounting a comeback.
Nadal seized back control with a break of serve at the start of the fourth and with the clock having ticked past midnight he finished off the match in a hurry.
Clinical Zverev eases into fourth round
Alexander Zverev did not have it all his way but eased into the fourth round of the Australian Open without dropping a set after a 6-3 6-4 6-4 victory over Romanian qualifier Radu Albot on John Cain Arena.
The world number three, still seeking the Grand Slam title that many have predicted for him, struggled with his serve at times but was always in full control as he set up a clash with Canadian Denis Shapovalov.
Albot, who plays much of his tennis on the second-tier challenger circuit, made a contest of the match but was unable to match the quality of the German's play in the decisive moments and failed to convert any of his five break points.