South Korea’s Chung Hyeon played superbly to beat Novak Djokovic at the Australian Open as the six-time champion struggled with injury.
Chung, 21, won 7-6 (7-4) 7-5 7-6 (7-3) to become the first Korean player to reach the last eight at a Grand Slam.
He will face another surprise quarter-finalist after American Tennys Sandgren upset fifth seed Dominic Thiem.
Djokovic, 30, had treatment to his right elbow after the first set and was visibly in pain at times.
“Unfortunately, it’s not great,” he said afterwards.
“Kind of end of the first set it started hurting more, so I had to deal with it until the end of the match.”
The Serb, seeded 14th, missed the second half of the 2017 season with an elbow injury, and was making his return to competitive action in Melbourne.
“I was hoping I can go through [the tournament],” he added.
“But I don’t want to talk about my injury tonight because then I’m taking away Chung’s victory, the credit that he deserves.”
Djokovic made it through three rounds but could not cope with a brilliant performance from Chung, while at the same time clearly struggling physically.
Chung’s ability to turn defence into attack and prevail in epic rallies was reminiscent of Djokovic himself.
“When I’m young, I’m just trying to copy Novak because he’s my idol,” said Chung.
Djokovic fights hard in defeat
Djokovic battled back from 4-0 down in the first set, 4-1 down in the second and 3-1 in the third, but eventually succumbed to an irrepressible opponent.
Despite his struggles, the former world number one made plenty of chances, but the unseeded Chung saw off 14 of 19 break points, while Djokovic ended with 57 errors to 36 winners.
It looked as though the match might be cut short when Djokovic called for the trainer after losing the first set, and again when he screamed in pain while lunging at the baseline as he fell 4-1 behind in the second.
By midway through the second, the Serb was sitting on his chair with a towel over his head, such was his frustration.
Again he fought back to level at 4-4, but again the pressure told and he netted a forehand to fall two sets down.
The third set followed a similar pattern and Chung missed a potentially decisive chance when he failed to return a second serve at 4-4 and break point.
Djokovic was now urging the crowd to carry him through, testing Chung’s nerve at 5-5, 0-30, but the Korean responded magnificently and forced a second tie-break.
Another lead disappeared as Djokovic fought back from 0-3 to level, but a miraculous hooked forehand winner put Chung 5-3 in front, and it was his turn to play to the crowd.
This time there was no Djokovic fightback, and Chung closed out the win of his life after three hours and 21 minutes.
“I didn’t know how I’d win this tonight,” added Chung. “I was just honoured to play against Novak, and happy to see him back on the tour.”
Future uncertain for Djokovic
After six months out undergoing painstaking rehabilitation, but opting against surgery, Djokovic must now reassess the way forward.
Andy Murray also missed the second half of last season through injury and attempted to return in Melbourne, but in the end he withdrew before the tournament and had hip surgery.
Asked about his next move, Djokovic admitted: “I really don’t know.
“It’s frustrating, of course, when you have that much time and you don’t heal properly.
“But it is what it is. There is some kind of a reason behind all of this. I’m just trying my best obviously because I love this sport.
“I enjoy training. I enjoy getting myself better, hoping that I can get better, perform and compete.”
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BBC tennis correspondent Russell Fuller:
When Djokovic was a set and 4-1 down, and hindered by the return of elbow pain, it appeared a Chung victory may have a hollow ring to it.
Far from it. Djokovic showed enormous heart to turn the match into a genuine contest, and gave Chung a stage to showcase his mesmerising skills.
The 21-year-old moves fantastically, and exhibits remarkable elasticity as he stretches for balls which at first appear just out of reach. Djokovic was his idol growing up, and his style has been strongly influenced by many hours in front of the TV watching the Serb.
Chung also showed the mental fortitude to win two sets in a tie-break, just when it looked as if the six-time champion had reeled him in.
The 21-year-old tends to keep a low profile in the locker room, but he showed off his improving English in an on-court interview after the match. He was more than ready to play another couple of sets, he told Jim Courier – pointing out that he’s quite a bit younger than Djokovic.