On Saturday evening, six-year-old Tara Djokovic brought her storybook with her into the Centre Court player box – a collection of fairytales, with a unicorn on the cover. Meanwhile, her father embarked on the third chapter of a required seven in his attempt to fashion the most improbable yarn of his own.

With his quest to win an eighth Championship here mere weeks after surgery on his right knee, Novak Djokovic has devised a plot to stretch credulity – an adventure beyond wisdom or reason, which he is determined to make fact.

Alexei Popyrin was the latest to attempt to halt the Djokovic odyssey, and just for a while it looked as though the world No.47 might do it. On the home soil of Australia this year, “Pop” took the seven-time Wimbledon champion to four sets; but on this occasion he could manage no more than a repeat.

As the clock ticked past three hours, Djokovic slew the latest dragon barring his way to the grail 4-6, 6-3, 6-4, 7-6(3). He appeared less physically drained and more mentally resourceful than in his second round win over Jacob Fearnley. Holger Rune awaits in the fourth round.

“Each match it’s getting better,” said Djokovic. “My confidence in my movement, especially in extremes when reaching and sliding – I definitely felt better than in the second round.

“I stepped it up and that’s one of the best tiebreaks I’ve played this year. Hopefully, the trajectory will keep going.”

The opening set of this third round was conducted in a strange atmosphere, as if each player was clutching a Ming vase and feared dropping it.

Djokovic – carrying his Vase Of Injury, and needing to protect it at all costs – produced a necessarily authoritative statement to start, by monopolising 11 of his opening 12 service points. Popyrin almost stumbled with the Vase Of Opportunity during a hesitant hold of serve mid-set, before suddenly cornering the No.2 seed into error for the first break point.

Djokovic failed to put away a smash, and could only watch as 24-year-old Popyrin carved a dazzling passing winner. The Centre Court came alive with a roar of appreciation.

Minutes later Djokovic had a chance to pass Popyrin at the net for break point to level, but instead flubbed it wide for set point. On his second serve, 'Pop' plopped the ball into the corner of the target area, and the set was gone.

But a pause to close the roof allowed Djokovic to regroup, and from that point on it was as if the first set simply never happened. The Serb rebooted the aggression and the match seemed to come into focus for him.

It was not that he scampered about the court entirely unhindered as in days of yore. But he closed out the second set with the 1,000th ace of his Wimbledon career; in the third, his serve became so impenetrable that he lost just two points on it.

Into the fourth Popyrin held fast on his own delivery, and waited for his moment as the passing of time exerted greater demands on Djokovic’s knee. But it was the Australian who could not stay the course in the breaker.

So the ballad of Djokovic rolls on, and here’s the conundrum at its heart. He has chosen to play through his post-operative recovery because he knows that at the age of 37, his remaining opportunities for Grand Slam glory are finite; but by choosing to play through his recovery, he is hindering his own likelihood of success, which was, in any case, more difficult precisely because he is 37.

In short, he is attempting something sufficiently extraordinary that success would make him a near-mythical creature, not unlike the one on the cover of six-year-old Tara’s book of fairytales.

Night had fallen outside the Centre Court by the time this match was done. It will be Monday when the next chapter of The Unicorn Conundrum by Novak Djokovic weaves its spell.

Bedtime, children. Sleep well.