An ailing Novak Djokovic crashed out of the Australian Open in the fourth round as up-and-comer Hyeon Chung clinically took advantage of the six-time champion's elbow injury to win 7-6, (7-4), 7-5, 7-6, (7-3).

The Serbian, who also struggled with his hip in the third round, was on the back foot from the start and failed to claw back the first set before suffering further at the start of the second.

Djokovic's fighting spirit never wavered, but he could not shake off NextGen champion Chung, who was unrelenting en route to claiming the biggest win of his career.

Chung – the first Korean male or female to reach a grand slam quarterfinal – said prior to the match he would "just be happy to share the court with Novak", but he was far from starstruck and an outstanding performance made him a deserved winner — albeit Djokovic, who missed six months before returning to play in Melbourne, was undoubtedly hindered by his injury.

The 21-year-old will now face another shock quarterfinalist in Tennys Sandgren on Wednesday.

A series of unforced errors, including numerous double faults, allowed Chung to break Djokovic's serve twice and move 4-0 up in the first set, before the former world number one came roaring back.

Three successive games piled the pressure on Chung and errors crept into the youngster's play as he served for the set, but he battled through to the tie-break and recovered his momentum to take the set.

It was clear Djokovic, wearing a protective sleeve on his right arm, was struggling with his elbow as he repeatedly failed to hold serve and he received treatment before the second set.

Chung held his nerve in a grueling first game and broke the 14th seed en route to building a 3-0 lead.

As in the first set, Djokovic's fighting spirit came to the fore as he drew level, but Chung again showed great resolve and he moved two sets ahead when a stunning rally ended with the groaning 30-year-old finding the net.

A topsy-turvy third set followed, bringing the crowd to its feet as four of the first five service games were broken to leave the pair neck and neck.

Both players missed big opportunities to then take control of proceedings and a number of poorly telegraphed drop shots from the world number 58 ensured Djokovic remained in the match.

But Chung kicked off the tie-break with two superb points and, although again there was a strong response, he continued to confound Djokovic with some astounding returns to seal a huge win.

STATISTICAL BREAKDOWN
Chung bt Djokovic [14] 7-6 (7-4) 7-5 7-6 (7-3)

WINNERS/UNFORCED ERRORS
Chung – 47/37
Djokovic – 36/57

ACES/DOUBLE FAULTS
Chung – 1/2
Djokovic – 2/9

BREAK POINTS WON
Chung – 6/10
Djokovic – 5/19

FIRST SERVE PERCENTAGE
Chung – 67
Djokovic – 62

PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Chung – 65/47
Djokovic – 65/39

TOTAL POINTS
Chung – 138
Djokovic – 128