Injury affected six-time winner Djokovic as he was beaten by Hyeon Chung in straight sets, while Tennys Sandgren got the better of Thiem after an entertaining five-set battle.

Djokovic's challenge ended at the hands of Chung, with the Korean rising to the occasion to beat his "idol" 7-6 (7-4) 7-5 7-6 (7-3).

A hip complaint had hindered former world number one Djokovic in the third round and it quickly became clear that his right elbow, covered in a protective sleeve, was going to affect his chances of reaching the last eight.

Even then, the Serb was perhaps unfortunate to come face to face with an outstanding young player who possessed the talent to punish his every error.

The match may only have lasted three sets, but it thrilled the Melbourne crowd and there was a great deal of mutual respect as the defeated Djokovic approached Chung at the end.

If Djokovic's defeat could be attributed to his injury problems, there was no excuse for Thiem as he was stunned by Sandgren.

The world number 97 triumphed 6-2 4-6 7-6 (7-4) 6-7 (7-9) 6-3, becoming the first player since Nicolas Escude in 1998 to make the last eight of the Australian Open on his main-draw debut.

Sandgren later pondered if he could be dreaming, but he must now prepare for a quarter-final against Chung in which the ATP rankings suggest he should at least have a fighting chance.

Meanwhile, defending champion Roger Federer had no such trouble as he cruised past Marton Fucsovics.

That victory set up a last-eight clash with Tomas Berdych, who was similarly dominant against Fabio Fognini and will now look to finally beat Federer in Melbourne at the fifth time of asking.