|Australian Open 2017|
|Venue: Melbourne Park, Melbourne Dates: 16-29 Jan|
|Coverage: Daily live commentary on BBC Radio 5 live sports extra; live text on selected matches on the BBC Sport website; TV highlights on BBC Two and online from 21 January.|
Novak Djokovic and Andy Murray have so much shared history.
And now, in the space of just four days in Melbourne, the world's top two players have both been on the receiving end of upsets almost without parallel in the past 10 years.
Former players were cheering Mischa Zverev on from the locker room - not because of any antipathy towards Murray, but because his opponent was playing the style of tennis many of them used to play to great effect.
Serving and volleying against the Briton seems counter-intuitive. Along with Djokovic, he is the best returner in the world - and if he does not manage to pass you, then he is more than likely to send a top spin lob fizzing over your head to within inches of the baseline.
But Zverev served superbly, and volleyed even better, again and again and again. The German hit some astonishing returns and made short shrift of Murray's second serve. And when the pressure started to rise, his level did not start to fall.
Pinned behind the baseline too frequently for comfort, Murray started missing more regularly. The Scot was unable to turn the tide or summon up the aggression that served him so well in the second half of last season.
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Andre Agassi addressed this subject before the match. The four-time Australian Open champion was very complimentary about Murray in a video link to Melbourne Park on Saturday, as he explained how the 29-year-old could improve still further.
"I have always sort of talked about Andy as a person that has never really utilised his game to his maximum potential. He's so good at certain things that it almost makes him a bit indecisive," Agassi said.
"If you actually minimised his defensive skills just 5%, he might even actually be a better player.
"He puts himself through unnecessary wear and tear on a court, because his offensive upside is, I think, still more than he shows."
Murray says he will now reflect on whether he could have done anything differently to prepare for the first Grand Slam of the year. He only had time for two weeks off after a frenetic end to last season, and must now balance the need for rest with his instinctive desire to play in Great Britain's Davis Cup first-round tie in Canada the week after next.
Murray suggested in the immediate aftermath of defeat that he intends to play in Ottawa, but his coaching team may well argue he should take a longer break before heading to Dubai in late February. The first two Masters events of the year follow in Indian Wells and Miami.
There is no immediate threat to Murray's world number one ranking - he will be 1,715 points ahead of Serb Djokovic when the list is refreshed at the end of the Australian Open.
He is certain to be number one until at least May because he has just a handful of ranking points to defend between now and the start of the clay court season.
Can anything further be read into the early exits of both Murray and Djokovic, who will both have turned 30 by the time the next Grand Slam is staged at Roland Garros in four months?
Ageing players are once again doing very well at this Australian Open, with half of the 12 men left in the draw on Sunday night older than the pair of them.
And yet in the modern era, men have found it tricky to win Grand Slam titles in their thirties. Stan Wawrinka and Agassi have each done it twice, but even Roger Federer has managed it only once.
Mats Wilander, who won the last of his seven Grand Slam titles at the age of 24, explains why it can become harder to find the consistency required over seven rounds.
"You have good days and you have bad days when you get older," Wilander told BBC Sport.
"You don't have to call on anything when you are younger - it's just there naturally. You don't worry about the consequences, you just play and you fight until the bitter end. I think the mind gets in your way when you get older."
Along with Federer - who will not now have to face Murray in the quarter-finals - it may be Raonic who takes most heart from Sunday's events.
You will not find him at the net as often as Zverev, but he did add the 1996 Wimbledon champion Richard Krajicek to his team in December with the explicit intention of trying to move forward on a more regular basis.
We are a long way from declaring a new serve-and-volley era, but Melbourne Park's quicker courts have contributed to an enthralling first week - unless, that is, you happen to be ranked number one or two in the world.