The Australian Open women's draw was blown wide open on Sunday after world No 1 Iga Swiatek was stunned in straight sets by Elena Rybakina in the fourth round, before Jelena Ostapenko defeated Coco Gauff.
In a battle between the two most recent Grand Slam champions, it was Wimbledon winner Rybakina who emerged victorious, claiming a 6-4, 6-4 victory inside Rod Laver Arena to advance to the quarter-finals.
Top seed Swiatek, who won Roland Garros and the US Open last season and was heavy favourite to win her fourth Grand Slam in Melbourne, joins second seed Ons Jabeur in exiting Melbourne Park unexpectedly early.
"It was a really tough match and I really respect Iga," said Kazakhstan's Rybakina, the 22nd seed. "She's a young player and think she played really well. It's a big win and I'm just happy to get to another round."
Rybakina will face Ostapenko in the quarter-finals after the Latvian, French Open winner in 2017, defeated American seventh seed Gauff.
Swiatek led 40-0 on her opening service game and 15-40 on Rybakina's delivery in the next, but it was the 6ft (1.84m) Russian-born player who showed her resilience and power to win both for an early 2-0 lead.
The Pole composed herself to hold in the next and then went on the attack, creating three break points and converting the first when Rybakina went long to level the set at 2-2.
At 3-3, 30-30, Swiatek's first double fault gave Rybakina another chance which she seized with a sizzling backhand crosscourt return. The Wimbledon champion comfortably served out, powering down her fourth ace on her first set point to move ahead after 42 minutes.
Swiatek stepped up at start of the second set, attacking off her forehand and broke immediately for 2-0 to chants of "Iga, Iga" from a small, but noisy, contingent of Polish fans clad in red and white.
The cries proved short-lived, though, as Rybakina broke to love at 1-3 as Swiatek's first serve deserted her.
Rybakina, by contrast, was now firing down serves with power and accuracy, her fifth ace helping her to level at 3-3.
"I think I was serving good and just struggling a bit on one side," Rybakina said. "But in the important moments I played really well and that made the difference."
Swiatek had won the pair's only previous meeting in straight sets at Ostrava in 2021, but history counted for nothing against the confident Kazakh who forced Swiatek to save two break points at 4-4.
A sixth forehand winner of the match from Rybakina created a third, which she took when the Pole netted and served out with ease to take the match.
Over on Margaret Court Arena, 17th seed Ostapenko ended Gauff's unbeaten start to the season with a 7-5, 6-3 victory to reach the Australian Open quarter-finals for the first time.
"I knew she's such a great player, super young and she's playing really well but I really had nothing to lose," said Ostapenko, who won her fifth WTA Tour title at the Dubai Duty Free Tennis Championships last year.
"I just went there and tried to show my best and try to fight for every point and to make it hard for her and I'm really happy with the way I played."
Ostapenko, whose last Grand Slam quarter-final came at Wimbledon in 2018, has endured some tough injury-hit years since and had never before beaten a player ranked inside the top-10 at the Australian Open.
"I was trying to stay positive all the time," Ostapenko, 25, said. "And I knew I have to play aggressive, even if I miss some balls.
Gauff had not dropped a set on the way to the last 16 and the match was a tight affair, with little to choose between the pair, but it was Ostapenko who played the crucial points better, pouncing at the end of each set. She broke Gauff at 6-5 to take the first, then again at 4-3 in the second.
"At the end, I think I kept her under so much pressure and it brought me a win," said Ostapenko.