Novak Djokovic, who has won the Australian Open six times, will not be in the final this year.
The Serbian star was knocked out in the fourth round by Hyeon Chung, a 21-year-old South Korean who beat him in three sets on January 22.
The 58th-ranked Chung defeated Djokovic 7-6 (4), 7-5, 7-6 (3) and will face little-known American player Tennys Sandgren in the quarterfinals.
Djokovic, 30, was off the tour last year with an elbow injury.
He said he did not decide to play in the Australian Open until shortly before it started.
Two years ago, Djokovic beat Chung in straight sets at the annual tournament in Melbourne, Australia, one of the four tennis Grand Slams.