Rivals now have more belief, admits defeated Djokovic

Fallen Grand Slam king Novak Djokovic admitted opponents now believe he is more vulnerable following his stunning second-round exit from the Australian Open.

The six-time winner and 12-time Grand Slam champion crashed out to unheralded Denis Istomin in five sets on Thursday in the world number two's earliest exit from a major since Wimbledon 2008.

Djokovic's stuttering start to the new season comes after he lost the world number one ranking he had held for 122 weeks from 2014 to Britain's Andy Murray in November.

He also relinquished his Wimbledon and US Open titles and was eliminated in the first round of the Rio Olympics by eventual champion Juan Martin Del Potro of Argentina.

The 7-6 (10/8), 5-7, 2-6, 7-6 (7/5), 6-4 loss to the 117th-ranked Istomin will only raise more questions about Djokovic's ability to stay at the top after dominating tennis for the last six years.

Asked if opponents have started to believe more over the last six months that he was beatable, Djokovic said: "Sure. They wouldn't be playing against me or any other opponent or any other tournament, for that matter, if they don't believe that they can win.

"They go out and they try their best. Today Denis, surely he was an underdog, but he didn't show any nerves in the big moments.

"Everything came together. It was the right moment for him, the right day. He was better."

Djokovic's stunning defeat ends a phenomenal run of success in Melbourne where he won six Australian Open titles in six finals.

- 'What can I do?' -

"I'm not used to losing in Australian Open second round," he said. "I've always played so well. Throughout the last 10 years, I've won six titles here.

"This court has been so nice to me. I enjoyed it very much. Of course, it's disappointing. But the end of the day I have to accept it."

Djokovic denied there was any hangover lingering from his breakthrough French Open victory at Roland Garros last June, and the underwhelming second half of last season which ensued.

"I don't know. I didn't reflect on that at all. I started a new season, a new year, as everybody else. I forgot about it, in a way. It's not affecting me," he said.

Djokovic added: "I started the season very well. Again, it's a tennis match. On a given day, you can lose.

"I mean, nothing is impossible. There are over a hundred players playing in the main draw.

I guess the quality of tennis keeps rising each year. Everybody becomes more professional. I guess they improve. They get better on the court.

"What can I do? I did try my best till the last shot, but it didn't work."

Djokovic's shock defeat comes after he parted ways with Grand Slam great Boris Becker as his coach last December after three years working together.

At the time of the split Becker criticised Djokovic for not training hard enough.

"He has not spent as much time on the practice court as he should have in the last six months and he knows that," Becker said.

"Success doesn't come by pushing a button. You have to work your butt off because that is what your opponents are doing."