Djokovic stunned by Tipsy

Djokovic admitted he was in poor form following his roasting by David Ferrer earlier in the week, but he started brilliantly to find his old shot-speed in taking the first set without facing a break point.

But the Serbian superstar appeared to tire badly, making several unforced errors and dropping serve to Tipsarevic twice in each of the final two sets, including his last service game as the world number nine broke to 30 to win the match.

The result left Djokovic needing already-qualified David Ferrer to beat Tomas Berdych in the late match, but the Czech won 3-6 7-5 6-1 to secure a semi-final spot at the expense of the world number one.

While Djokovic was nowhere near his best, the bespectacled Tipsarevic played close to the top of his game as he found some devilish angles with his drop shots in particular.

"There were a lot of ups and downs for both Nole and me," Tipsarevic - who was asked to play in London after world number three Andy Murray withdrew injured - said after a first Tour victory in four matches against his friend.

"I started the season (ranked) 49th and if someone told me this was how I’d finish 2011 I would have taken it in a heartbeat.

"I’m really happy to be in London, it’s a great event and a great crowd and I hope I can be here next year."

The pair are hitting partners and close personal friends, with their places in the top 10 remarkable given the size and relative lack of resources in their homeland.

Tipsarevic joked that Djokovic may cancel their planned post-season holiday after the defeat.

"During the match I felt proud to see both Serbian flags at the O2 Arena in Great Britain. We had a lot of difficulties in the past and everything we have achieved gives me a great feeling," he added.

"We are actually scheduled to go on vacation together after this event. I have to talk to him but I don’t think anything is going to change."