Novak Djokovic's problems came to an explosive head at the Shanghai Masters and the Serb now faces being knocked off world number one if he can't find a quick solution.

Djokovic arrived in Shanghai insisting mental equanimity, rather than titles, was his goal after a rough patch of form prompted a bout of soul-searching.

The man who has dominated tennis for the past two years even resorted to humming a song in a bid to keep calm as he was taken to three sets by qualifier Mischa Zverev.

But Djokovic's avowed cool-headedness evaporated in a stormy semi-final upset against Roberto Bautista when he smashed his racquet, ripped his shirt and raged at the chair umpire.

Worse for Djokovic, second-ranked Andy Murray cruised into the Shanghai final without dropping a set and is in position to put further heat on his number one spot.

"It's not yet over. There are a couple of big tournaments still along the way: Paris and London," Djokovic warned.

"I'll try to get ready for the indoor season where I always, in the last couple of years, played pretty well. I'll try to get better."

Recent months have not been kind to Djokovic, who has suddenly and mystifyingly lost his way after winning six of his 12 Grand Slam titles in a stunning two-year period.

He was on top of the world after completing a career Grand Slam at the French Open in June, becoming only the third man to hold all four major titles at once.

But his 30-match winning streak at Grand Slams came to a shuddering halt when he was well beaten by 41st-ranked Sam Querrey in the third round at Wimbledon.

Order was restored when Djokovic won in Toronto but he then crashed out of the Rio Olympics' first round in tears and was bullied in the US Open final by Stan Wawrinka.

'Not as dominant'

Wrist and elbow injuries have played a role and Djokovic has also admitted to struggling with "private issues".

His collapse could reshape the pecking order once again with Murray now the foremost player of the crumbling 'Big Four', which also includes injury-hit Roger Federer and Rafael Nadal.

Murray, a contemporary of Djokovic and a sparring partner since they were teenagers, said he didn't find it surprising that the Serb's superb run had taken its toll.

"It takes so much effort and work to be making finals almost every single week for two years. It's a really, really hard thing to do," Murray said.

"It's maybe normal if he's mentally a little bit tired or trying to find the next thing to achieve after what he did at the French Open, as well.

"I'm sure he will get it back. But it's just normal to have a period after what he's done the last few years where he's maybe not as dominant as he was."

Djokovic, who retreated from his Monte Carlo residence to his native Belgrade as the storm clouds gathered, will seek solace in family comforts before resuming action at the Paris Masters in two weeks' time.

"I'm going to celebrate my son's second birthday. That's an event I look forward to. I'm going to do a lot of things off the court, plenty of things off the court," he said.

He added: "I had to experience this sooner or later. I knew I could not go on playing at the highest level for so many years all the time.

"It's good to experience this so I can hopefully get better in the period to come."