Six-times champion Novak Djokovic bowed out of the Australian Open in the fourth round as relentless South Korean Chung Hyeon ground him down to claim a stunning 7-6(4) 7-5 7-6(3) victory on Monday.

The 21-year-old Chung, ranked 58th in the world, proved an immovable object, absorbing everything the former world number one could throw at him and returning it with interest.

Djokovic, grimacing occasionally and flexing his elbow, dropped the opening four games and although he clawed back the deficit Chung took the opening set on the tiebreak.

Chung moved 4-1 ahead in the second set but again Djokovic recovered, only to falter when serving at 5-6, netting a forehand on set point after Chung had shown incredible defensive skills to stay alive in the rally.

Again Djokovic battled back from a break down in the third set to force a tiebreak but Chung refused to let the 30-year-old Serb off the hook.

Chung hooked a mind-boggling forehand winner past Djokovic to take a 5-3 lead in the tiebreak and when Djokovic netted a return it brought up three match points.

One was enough as Djokovic hit into the tramlines.

Chung will face unseeded American Tennys Sandgren for a place in the semi-finals.

Defending champion Roger Federer sauntered past Hungarian Marton Fucsovics to reach the 52nd grand slam quarter-final of his career where he will meet big-serving Czech Tomas Berdych.

Women's top seed Simona Halep shook off ankle pain to sweep past Japanese Naomi Osaka 6-3 6-2 in 79 minutes and stay in the hunt for a maiden grand slam title.

Halep will meet Karolina Pliskova in the quarter-finals after the Czech sixth seed rallied from a set down to see off compatriot Barbora Strycova in the day's last match.

Former champion Angelique Kerber fell back on raw power to overcome the unorthodox game of world number 88 Hsieh Su-wei 4-6 7-5 6-2 and reach the last eight where she will meet U.S. Open finalist Madison Keys.

Novak Djokovic (right) congratulates Chung Hyeon at the end of their match in Melbourne.