World number one Simona Halep crashed to a straight-sets defeat against unseeded Ashleigh Barty in the second round of the Sydney International on Wednesday.
Halep, playing in her first tournament since a back injury cut short her 2018 season, lost 6-4, 6-4 in 87 minutes with the result dealing a blow to her Australian Open preparations.
Australian Barty, who is ranked 15th in the world, fired 26 winners and won four out of seven break points as she recorded her first victory over a reigning world number one.
The 22-year-old Barty faces either Elise Mertens or the winner of the first round clash between Anett Kontaveit and Monica Puig in the quarter-finals.
Trick-shot Tomic bamboozles Kyrgios with bizarre match point serve
Bernard Tomic secured a controversial-yet-comical victory in an exhibition match against compatriot Nick Kyrgios at the Kooyong Classic on Wednesday when the Australian hit an ace on match point with an underarm serve from behind his legs.
Serving for the contest in the second set, world number 85 Tomic moved into his service stance before chipping one ball over the net while still bouncing another, catching Kyrgios, the umpire and spectators completely off guard.
Kyrgios was left laughing and shaking his head in disbelief as the umpire announced "game, set and match" with a 6-3, 6-4 scoreline after a few moments of deliberation in the Australian Open warmup encounter.
"I don't think there's ever been a player like BT (Tomic)," Kyrgios, another of Australia's more mercurial talents, told reporters.
Tomic has slipped down the world rankings from a career high number 17 in recent seasons, but has improved recently and won his first title in three years at the Chengdu Open in September.
"It is great to see him back out here as I know he was going through some rough times," world number 51 Kyrgios, who himself has struggled for consistency, added.
"He won a title last year and it looks like he is carrying a bit of momentum which is good to see... he looks happy, he looks healthy. That's the main thing... you never want to see a talent like that go down and keep being down."
While Kyrgios saw the bright side of Tomic's sneaky service winner, Australian Olympic hockey player Georgie Parker, who was watching in the stands, was less than impressed and took to Twitter to express her dismay.
"It's an absolute joke. I'm paying money to be here and the two idiots aren't giving two shits," she wrote.
"It's an exhibition match but you can still bet on it... How this isn't match fixing is beyond me? Get these two off the circuit."
Tomic and Kyrgios will both feature at the Australian Open in Melbourne next week.
Top seed Isner beaten by Fritz in Auckland second round
Top seed John Isner suffered a 7-6(3), 7-6(5) defeat at the hands of fellow American Taylor Fritz in the second round of the Auckland Classic on Wednesday.
The big-serving Isner, ranked 10th in the world, fired 26 aces but struggled on his second serve as Fritz took full advantage to edge the match in an hour and 39 minutes.
"I really wanted to get the win on him. I knew I could," said Fritz. "We had a lot of close points and it just feels really good to get through that," world number 50 Fritz said.
The 21-year-old converted one out of three break points and saved three on his serve.
"I like to think that one of my strengths is playing under pressure and playing the big moments well," Fritz added.
"More often than not, the matches I lose, that's where I get let down. So I'm happy to start the year ... playing well under pressure and handling those big moments well."
Fritz will next face Briton Cameron Norrie, who overcame Joao Sousa 7-6(5), 6-4.
American Tennys Sandgren also advanced to the quarter-finals, beating third seed Marco Cecchinato of Italy 6-3, 6-3 to set up a meeting with Leonardo Mayer.
The Argentine saved five out of six break points to move past Matteo Berrettini 5-7, 7-6(5), 6-3.