Former world number one and six-time champion of the Australian Open, Novak Djokovic, was beaten in the fourth round of the competition by an unseeded competitor.
Hyeon Chung has become the first Korean player to make it to the quarter-finals of a Grand Slam.
The 21-year-old beat the 14th seed Serb 7-6 (7-4) 7-5 7-6 (7-3).
Djokovic, who has been side-lined with an injury since Wimbledon last year, required treatment to his right elbow after the first set and was visibly in pain at times throughout the match.
Chung will face American Tennys Sandgren, who was the victor in another fourth- round upset after beating fifth seed Dominic Thiem.