The six-time winner struggled for rhythm and lost 7-6 (10-8) 5-7 2-6 7-6 (7-5) 6-4 in four hours and 48 minutes.

It is the first time Djokovic, 29, has lost in the second round of a Grand Slam since 2008 at Wimbledon.

The result leaves world number one Andy Murray as favourite to win his first Australian Open title in Melbourne.

Britain's Murray, who has already reached round three, has lost five finals in the past seven years in Melbourne, four of them to Djokovic.

It is only the second time in seven years that Djokovic has lost to a player ranked outside the top 100 - his defeat by Juan Martin del Potro, ranked 145th, at the Rio Olympics in 2016 being the other occasion.

"He deserved to win. No doubt, he was a better player in the clutch moments," Djokovic said.

"Many things came together for him today and he's a well-deserved winner. There's not much I could do."