After six months away due to an elbow injury, Djokovic's return to court proved to be short-lived on Monday, after he was dispatched in straight sets at the Australian Open by a player whom very few people had heard of before.
"Welcome to the tennis world Hyeon Chung," American tennis star John McEnroe said at the end of a breathless match.
It was nothing like their previous encounter in 2016 when Djokovic easily saw off Chung in straight sets in the opening round of the Australian Open.
This time the South Korean dashed the Serb's hopes of reaching the last eight in Melbourne for a 10th time, beating Djokovic 6-7 (4-7) 5-7 6-7 (3-7).
"I didn't know if I was going to win ... but I was just honoured to play with Novak again," said Chung, who described Djokovic as his idol.
"He was the better player on court today and he deserved to win," said the former World number one, who was clearly in pain as he stretched for balls.
Where Djokovic goes from here will depend on talks with his medical team.
As for Chung, he becomes the first South Korean man to reach the last 16 at the Australian Open and will face American bolter Tennys Sandgren in the quarter-finals on Wednesday.