Denis Istomin.
Denis Istomin causes major shock in Melbourne after sending the champion packing Reuters

Defending champion Novak Djokovic has crashed out of the Australian Open after a shock second round defeat to Denis Istomin.

Djokovic, a six-time champion in Melbourne, had not gone out of the first Grand Slam of the year before the fourth round since 2006. His desperately poor run of form continues after a 6-7 7-5 6-2 6-7 4-6 defeat to a man ranked 117th in the world at the Rod Laver Arena on Thursday (19 January).

Djokovic had to come from a break down to force a tie break in the opening set but lost out to the challenger after an unforced error. While he came back to win the next two against the Uzbek wildcard, the Serbian appeared to pick up an injury during the early stages of the second set, immediately clutching his left leg before gingerly attempting to walk it off.

The six-time Australian Open champion took the lead in the third set but Istomin again pulled level in the fourth, sending the tie to a decider with a superb ace.

The 30-year-old grew in confidence in the fifth set, securing a decisive break in the fifth game with Djokovic visibly wilting. The 12-time grand slam winner was unable to find any answers as Istomin took control, netting another two forehands as unforced errors continued to rack up. A perfect serve down the middle from Istomin left the champion on the brink with Djokovic sending his next return long to seal his early exit.

The former world no.1 has lost just twice to players outside the top 100 in the past seven years. But in a telling indictment of his recent slump, both of those have come within the past six months having suffered defeat to no. 145 Juan Martin del Potro at the 2016 Olympic Games in Rio de Janeiro.

The Serb had sat atop the world rankings for 122 weeks before he was dethroned by Andy Murray in November last year. An alarming drop in form during the second half of 2016 saw him eliminated in the third round of Wimbledon by Sam Querry. After disappointment in Rio, Djokovic was then defeated in the US Open final by Stanislas Wawrinka, with Murray taking full advantage to replace him as the no. 1 force in men's tennis