Novak Djokovic graciously bowed out of his bid to win four Grand Slams in a calendar year but gave a hint of something being wrong after his shock Wimbledon exit to Sam Querrey.

The Serbian has been as close as there is to unbeatable for the best part of the last 18 months and arrived in London as the holder of all four men’s Grand Slam titles.

So good has he been that it was considered a formality by many that he would be the finalist from the top half of the draw and, in all likelihood a showpiece opponent for Andy Murray.

That did not account for a meeting with Querrey, the big-serving American who had previously reached the fourth round of a Grand Slam on just three occasions.

Djokovic never looked at his best in a Court One clash severely hampered by rain, and when even an overnight delay at two sets down could not fire him up properly, it became clear that something was amiss.

He went on to lose 7-6 (8/6) 6-1 3-6 7-6 (7/5), and while full of praise for his conqueror – who sent down 31 aces – his refusal to speak about what may have been troubling him left more questions than it did answers.

“Congratulations to Sam, he played a terrific match,” said Djokovic, who in revealing he would not face Britain in the Davis Cup later this month gave Murray another boost.

“He served very well, as he usually does. That part of his game was brutal today. Well done, he overpowered me.”

So unusual was Djokovic’s submission that the media felt moved to probe for reasons as to why. He was asked about the rain – which delayed this match three times – playing on Court One instead of Centre and his general demeanour.

“I don’t want to take anything out of victory from my opponent, I had my chances, served for the fourth set, led in the tie-break but wasn’t feeling the ball as I wished,” he said.

“It’s not a place and time to talk about it, the opponent was playing at a high level and deserved to win.”

Asked about the court, he said: “I’m more comfortable on Centre, because I’ve played 90 per cent of matches there. Naturally I am going to feel better on there.”

Asked again if there was something bothering him, and put to him that he had not looked himself during a morning practice, he said: “I don’t want to talk about it, please respect that.”

It was widely assumed that, having beaten Murray in the finals of the Australian and French Opens, the two would meet here too, with few tipping the Scot to beat him, so accustomed have fans and experts become to Djokovic’s success.

“I don’t think it (expectancy) played a big factor,” he said. “I knew it was going to be very close.

“It’s an amazing feeling to hold all four Grand Slams at the same time, but coming to Wimbledon I knew it wouldn’t be easy. I re-motivated myself but my best wasn’t good enough this year.”

Murray ensured there was only one sensational upset on Saturday afternoon as he saw off Australia's John Millman in straight sets.

While Murray was overcoming a spirited challenge from his 67th-ranked opponent, all eyes were on Court One and the remarkable downfall of Djokovic.

There was no escaping the news for Murray on Centre Court but he managed to put aside all thoughts of what might be to come and wrapped up a 6-3 7-5 6-2 victory.

The Scot is now favourite to add to his 2013 title but told BBC One: “I need to reach the final for (Djokovic’s) result to have any bearing on me.

“I have very tough guys in my half of the draw, especially in the next round.”

Murray will play either Nick Kyrgios or Feliciano Lopez in round four on Monday.

Should it be Kyrgios, Murray will be buoyed by the fact this victory made it 18 wins from 18 matches against Australians at tour level, although he was beaten by Kyrgios at the Hopman Cup in January.

His match against Millman officially lasted two hours and 11 minutes, but in reality was significantly longer thanks to the bizarre decision of tournament organisers not to keep the roof shut.

No sooner had they opened it following the conclusion of the previous match than rain began to fall and the covers came on.

It was then kept open but the players were forced off twice in quick succession at the start of the second set and the rest of the match was played under cover.

Millman was through to the third round at Wimbledon for the first time after knocking out 26th seed, and renowned grass hater, Benoit Paire.

Like many players these days, Millman has made his breakthrough in his mid-20s, although his progress was stalled by a serious shoulder injury.

During his recovery, the 27-year-old spent some time working for a friend’s finance company back home in Brisbane.

It was in his home town in 2013 that he played Murray for the first time and pushed him close.

There looked little chance of the same thing happening here when the Scot raced through the first three games in just seven minutes and he recovered from a minor blip to take the set comfortably.

The Scot would surely have hoped that being on Centre Court would protect him from the vagaries of the British summer but just one point into the second set rain began to fall and the players were forced off.

Only two points were possible on the restart before the weather intervened again and the roof was finally deployed, Beckham earning a big cheer for joining in the Mexican wave as the crowd waited for play to restart.

Murray struggled to find his rhythm on the resumption and Millman adopted a more aggressive attitude but the home favourite stepped things up and at 5-3 he twice forced set point.

He could not take either and at the change of ends a huge roar erupted as the Centre Court scoreboard showed Djokovic’s defeat.

Murray would have tried to put that out of his mind but his focus had certainly wavered as he lost the first three points serving for the set and was broken.

He had got dragged into a battle but, after 15 minutes and five break points on Millman’s serve at 5-5, he finally broke again and, serving for the set for a second time, made no mistake.

The relief of getting over the line in the second set allowed Murray to relax and he reeled off the first four games of the third before clinching victory with his eighth ace.