Becker and Djokovic parted ways last year after the 29-year-old failed to win Wimbledon, the Olympics or the US Open which led to him surrendering the world No.1 spot to Andy Murray.

Djokovic fell 7-6 (10-8) 5-7 2-6 7-6 (7-5) 6-4 to wildcard Istomin on Rod Laver Arena marking the first time he has been evicted from a grand slam before the third round since 2008.

Becker, a nine-time grand slam champion, criticised his former charge’s tactics throughout the five-hour epic.

“I’m really shocked that Novak Djokovic lost,” the two-time Australian Open champ said during Eurosport’s live coverage of the match.

“I thought he was playing much too defensive and never really took the initiative and never really fought for it.

“I absolutely never expected him to have trouble with Denis Istomin. No disrespect but Nole (Djokovic) is a six-time Australian Open champion.

“But I could tell in the first set he was way too defensive and way too passive. The first set in a three out of five match is always very important.

“In the fourth set again he was a bit lethargic and not playing at full power.

“Then once you’re in the fifth set anything can happen and credit to Denis, he kept his composure, he kept his nerve, he went a break up and kept serving well and hitting the lines so it’s well deserved.”