Rafael Nadal has backed long-time rival Novak Djokovic to bounce back from his surprise Australian Open defeat to Denis Istomin on Thursday.

Six-time champion Djokovic departed in the second round after a five-set thriller, Istomin coming from 2-1 down to send the Serbian crashing out.

The loss marked Djokovic's earliest grand slam exit since Wimbledon 2008 and leaves him with only one major crown to his name - a fall from grace after completing a career Grand Slam at the French Open last year.

Nadal labelled the defeat an "accident" and fully expects Djokovic to remain a threat in the men's game despite his dominance slipping over the past 12 months.

"What Novak did here is just amazing," he told a media conference. "Six victories here, six titles. For a lot of years he has been in the semi-finals, finals, and winning here. 

"[But it] is not possible to be in that situation every time.

"He played great a week and a half or two weeks ago in Doha, winning the title. So then today was probably an accident, that's all. He's playing well. 

"Everybody has the chance to lose when you go on court, no? We are athletes. We know when we are going on court we can lose and we can win. Everybody wants to win. Everybody has a good level.

"Today Denis played well. That probably was a combination that Denis played a great match and Novak didn't play his best. When this combination happens, then you are in trouble. Everything can happen. And happened."

Nadal had no such problems in his second round match as he cruised past Marcos Baghdatis 6-3 6-1 6-3, setting up a clash with Alexander Zverev.

The Spaniard said: "[I am] very happy for the victory. I think I can do things better, it's true. I need to have less mistakes, but in general I have been playing well.

"[Zverev] is a great player, he is one of the best players of the world, without a doubt, today. And he is a player that is for sure one of the next grand slam winners. He has a big chance to become the future world number one.

"He has all the shots: great serve, great forehand, great backhand, everything. He's a complete player.

"I know I have a very tough match, and I know I need to play my best if I want to have chances."