South Korea's Hyeon Chung played superbly to beat Novak Djokovic at the Australian Open as the six-time champion struggled with injury، BBC reported.
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 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."