Novak Djokovic's Enduring Brilliance: A Masterclass in Longevity and Heart

It is worth remembering that what you are watching is not normal.

It is not normal that a 39-year-old should beat an opponent 14 years his junior in five sets in the quarter-finals of a Grand Slam.

It is not normal that after five hours and 15 minutes, he is still chasing down every single shot that is pounded towards his racquet.

It is not normal that he is gliding and sliding and then charging around the baseline, running to the net to meet drop shots, and still sending down second serves at 122 mph.

But then, this is Novak Djokovic.

A 24-time Grand Slam champion, one major away from the all-time record. Arguably the greatest to ever do it. A man who thrives on proving the doubters and the critics wrong.

Under the lights of Centre Court, an epic battle played out. It was a match so engrossing it delayed the BBC News at 10. A packed crowd lived every moment.

They were first behind Auger-Aliassime, the underdog. Then it was Djokovic, the great, roared on after losing the third set.

They were split by the fifth set, but as Djokovic pulled away in the tie-break, the fans chanted his name. They stood and screamed as one as Auger-Aliassime spooned a backhand long to confirm Djokovic's victory.

"To be able to come out and play this level of tennis at that age... it's not normal. It's really not normal," Leon Smith, Britain's Davis Cup captain, said on BBC 5 Live.

"I know he spent a lifetime on his body, but to do this, the amount of work that we don't see must be astonishing.

"It is amazing. He deserves all the respect that he gets."

An exhausted but delighted Djokovic said afterwards that he "won that match with a racquet and a lot of heart".

It is a sentiment that sums up the latter half of his career. Djokovic's movement is still sublime, his shots still potent, but his body has not always held up.

Against Auger-Aliassime, an innocuous slide to a backhand led to him tweaking his left calf and needing a medical timeout.

His movement was hindered for the rest of the first set, particularly on serve, but he was helped on his way to taking the opener by a series of errors from the Canadian.

But five hours later, Djokovic was still moving around the court as well as ever.

"I've been watching this guy for 20 years and time and time again, in the biggest moments, he delivers," former British number one Tim Henman said on BBC TV.

"This is the response we have all come to expect from Novak Djokovic."

Moments like these are ones to be cherished.

Djokovic is the last player standing from the 'Big Three' era. It has taken the retirements of Roger Federer and Rafael Nadal for some to realise how special Djokovic is, and how lucky tennis is to have him.

Beyond Jannik Sinner and Carlos Alcaraz's generational rivalry, the ATP Tour struggles to have players challenging for the majors or to cut through and captivate the wider public.

Djokovic is the one still taking it to the youngsters. He beat Sinner at the Australian Open in Melbourne and took a set off Alcaraz in the final.

He has done what others cannot - beaten both players in recent years, despite them in theory having youth, power and speed on their side.

Asked afterwards if he is surprised by his level, Djokovic said: "Yes and no.

"I guess yes, at this stage that I'm still able to battle these young guys that have 15 years less than me, that I'm able to beat them at the tightest possible scoreline.

"In a sense, it is really a nice surprise. But at the same time, I always have the highest expectations for myself.

"I can be very self-critical, very hard on myself. But I try to enjoy the moments like this."

The question now is how much will his efforts cost him against Sinner in the semi-finals.

Last year, Djokovic fell late in his quarter-final and his movement was hindered for the rest of the tournament. Sinner, who had an elbow injury of his own, took advantage, and won in straight sets.

Afterwards, Djokovic said the reality of age and injuries had "hit me right now, the last year and a half, like never before".

He reached the semi-finals of all four Grand Slams last year, and had a niggle in each match. At this year's Australian Open, he benefited from a walkover and a mid-match retirement on his way to the semi-finals, where he beat Sinner.

But the five-set match against Sinner caught up with Djokovic in the final against Alcaraz and he faded after a dominant first set.

Djokovic will have two days to recover - but regardless, he has played the longest match of the tournament so far, while his opponent has not dropped a set in the past four rounds.

"I don't know what tomorrow brings. I still want to go at least one more step further," Djokovic added.

"But this was as good as a final for me. I gave it all that I had."