Young American Alex Michelsen caused the first big upset of the Australian Open by knocking out former finalist Stefanos Tsitsipas in the opening round.
Tsitsipas was beaten by Novak Djokovic in the final two years ago and is also a three-time semi-finalist, but he has struggled since reaching the quarter-finals of the French Open last spring.
He has now lost three grand slam matches in a row after a second-round exit at Wimbledon and first-round defeat at the US Open.
The Greek 11th seed threatened a comeback by winning the third set against Michelsen, but the talented 20-year-old, who reached the third round on his debut last year, held his nerve to claim a 7-5 6-3 2-6 6-4 victory.
"It was a difficult first-round match," said Tsitsipas. "I knew I was dealing with a pretty serious opponent because I've played him before and I have lost.
"So I knew I had to be on top of my game to try and win this match. I had a very slow start to the match.
"In terms of finding my movements and just dominating from the serve plus one, it wasn't really the way I'm expecting it to work. That led to some frustration and, let's say, insecurity in terms of approaching my game."
Tsitsipas admitted he does not know how he will get out of his current funk, saying: "The most frustrating part about losing in the first round of a grand slam is that you have way too much time to recover, and I would rather have the other way around where I don't have enough time to recover.
"Honestly, that's much, much better in terms of problem solving. It just sucks in a way that I'll be hanging around for quite a while now before my next tournament comes in. With my competitive nature, I feel like these type of things are not really ideal for me."
