One person who foresaw Novak Djokovic's shock demise at Wimbledon this year was no less an authority than Roger Federer.The holder of 17 grand slam singles titles and considered the greatest tennis player of all time, had expressed doubts about Djokovic's capacity to sustain his staggering sequence of major victories."Margins are small, and we get carried away in saying that it's impossible to beat him," said Federer, the seven-time Wimbledon champion. "But clearly, he's beatable. He cannot win 200 straight matches in tennis. It's not possible."The verdict was to prove prescient. Djokovic seemed weighed down throughout his match by the burden of trying to become only the second man after Rod Laver to secure the calendar slam. These anxieties also sank Serena Williams as she lost a chance of winning all four majors last year by losing at the US Open to Roberta Vinci, an opponent by whom she should never have been troubled.On Saturday Djokovic, the most remorselessly dominant player tennis has ever known, limped tamely out of Wimbledon. He was cut down by the brilliant serving of the American Sam Querrey in a stunning upset that brought his assault on the record books to an abrupt halt.There will be no "golden slam" with the world No1 thwarted in his aspiration to snaffle the full set of all four major trophies and an Olympic gold medal in the same year, a feat only ever accomplished by Steffi Graf. Instead, he beat the quickest retreat from Wimbledon on Saturday night, chastened and bewildered at how he had thrown it away.True, Querrey, the first American in three years to beat a world No1, served wonderfully, overpowering Djokovic at times. But there was no disguising that Djokovic was a pale imitation of his usual self, apparently struggling with a cold and quailing, perhaps, at the magnitude of the stakes he was striving for. ..