Defending champion Novak Djokovic came through a stiff test of his fitness as he moved into the Australian Open quarter-finals, but third seed Dominic Thiem was stunned by Grigor Dimitrov.
Bulgarian Dimitrov, a semi-finalist in 2017, dismantled the US Open champion of Austria 6-4 6-4 6-0.
World number one Djokovic, struggling with an abdominal injury picked up on Friday, beat Milos Raonic in four sets.
The Serbian eight-time Australian Open champion won 7-6 (7-4) 4-6 6-1 6-4.
"In any other tournament than a Grand Slam I would have retired from the event, but because it's a Grand Slam I wanted to give my best," Djokovic, 33, said.
"I didn't know if I was going to play or not. During the match it [the injury] was on and off, it's still not ideal but I can't complain and won against a great player. Hopefully it will be even better in two days.
"There was no preparation for this match, I used every single hour I had to recover and put myself in a position where I could compete. My physio has done a great job and I want to thank my team and the ATP physios for being here for me.
"I've definitely been fitter but I'm taking each day at a time and for me training is just recovery."
He will play sixth seed Alexander Zverev after the German beat Djokovic's compatriot Dusan Lajovic 6-4 7-6 (7-5) 6-3.
Dimitrov, the 18th seed, will face Russian qualifier Aslan Karatsev, who stunned Felix Auger-Aliassime as his dream Grand Slam debut continued.
Injured Djokovic wins again
Top seed Djokovic had expressed doubt over whether he would be fit in time to face Raonic, saying he thought he had torn a muscle when he slipped during his five-set third-round win over American Taylor Fritz.
But, with the right side of his chest strapped up, he was able to move more freely on Sunday than he had done two days earlier when he had been repeatedly limping and needed courtside medical treatment.
This victory continued Djokovic's perfect record against Canadian Raonic, who has now lost all 12 of his matches against the Serb and been eliminated by him from the Australian Open for the third time after losses in 2020 and 2015.
Djokovic took the opening set on a tie-break but the 14th seed, who himself needed a medical timeout to have his ankle strapped up, broke in the fifth game of the second set after failing to have a single break-point chance in the first set.
But it did not take long for the 17-time Grand Slam champion to regain control of the match as he broke in the fourth game of the third set, before dominating the rest of that set.
He then broke late on in the fourth set to clinch the victory as he stays on course for a third successive Melbourne success.
A 'real bad day' for Thiem
Thiem, last year's runner-up, said he had "physical issues" in his shock loss to Dimitrov, but also added that he did not "want to find any excuses".
"I'm not a machine. I mean, sometimes I would like to be, but there are really, really bad days," the third seed said.
"I think a combination of some things, some little physical issues, plus a real bad day, plus the fact that he's a great player. So a combination of those three things, and a result like that can happen."
Thiem came through a gruelling five-setter against Nick Kyrgios on Friday to reach this stage, fighting back from two sets down, but there was no such reprieve against Dimitrov on Sunday.
The Austrian looked to have taken the momentum with a break in the opening set, but Dimitrov immediately broke back and won four successive games on his way to taking the first set.
It was the same pattern in the second set, a Thiem break followed by a revival from the 29-year-old, before he motored to victory in the final set to win in just over two hours on Rod Laver Arena.
"I was entirely trying to focus on what I was doing," said Dimitrov, a former world number three. "He might have struggled with something, I don't know, but I give myself credit for staying focused.
"Throughout every season you have one of those matches, you just keep the ball rolling, and today was one of those."
Qualifier Karatsev's fairytale run continues
Russian qualifier Karatsev came from two sets down to pull off yet another stunning victory to reach the quarter-finals.
The 27-year-old world number 114 beat Canadian 20th seed Auger-Aliassime 3-6 1-6 6-3 6-3 6-4.
With victory over eighth seed Diego Schwartzman in the previous round, Karatsev has been the surprise package at this year's event at Melbourne Park.
He is the first man to reach a major quarter-final on debut for 25 years.
Dogged by injury during his career, Karatsev had failed in nine previous attempts to reach a Grand Slam main draw, but at the ATP Cup earlier this month he was described by world number four Daniil Medvedev as Russia's "secret weapon".
He has more than proved this, having reached the fourth round without dropping a set before mounting an incredible comeback against Auger-Aliassime in the first five-setter of his career to set up a last-eight meeting with Dimitrov.
"I'll be ready for everyone," said Karatsev, who is the first man since Alex Radulescu in 1996 to make it to the last eight on their Grand Slam debut.
Meanwhile, British interest in the singles might have ended with Cameron Norrie's exit to Rafael Nadal on Saturday, but there was a mixed doubles win on Sunday in Melbourne.
Neal Skupski teamed up with Slovenia's Andreja Klepac to beat Australian pair John Peers and Belinda Woolcock 6-2 5-7 (12-10) in a match tie-break in the first round.
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