Novak Djokovic goes into his sixth Australian Open final as mercurial as he is potent. He will surely start favourite because he always does, yet he carries with him a hint of vulnerability to give his opponent a scintilla of hope.

As difficult as it is to compute how Djokovic could struggle against Gilles Simon over five sets for four-and-a-half hours four days earlier then get halfway towards what looked to be developing into a public execution of Roger Federer before mysteriously losing his way on Thursday night, the Serb has been defying logic for years.

He is like a diamond: almost impossible to cut but prone to shattering when the right incision is made, with the right tools. Federer had the tools. He knew what to do. But he couldn’t keep it up. Djokovic won 6-1, 6-2, 3-6, 6-3 in two hours and 29 minutes, numbers that hardly tell the story.

“It was very close,” Djokovic said courtside, “and that was the case here against Simon in the fourth round. You play a lot of mind games with yourself but, at the end of the day, your convictions are stronger than your doubts. Right now I feel I am at the peak of my career and I want to cherish every moment.

“This was the first grand slam I won, back in 2008. Each time I come back I have this beautiful memory. Over the years I have played some of my best tennis here.” And, for moments at least, some of his worst.

Djokovic does things on a tennis court that sometimes make little sense: such as surviving a semi-final of four hours and 50 minutes against Andy Murray here four years ago, then beating Rafael Nadal in the final 36 hours later in a match that went five hours and 53 minutes, the longest final in grand slam history. As Murray has remarked since, he remains in awe of that performance, as his own efforts had left him barely able to get out of bed the next day.

But Djokovic is special in many ways. His off days are rare. His best days are awe-inspiring. For an hour-and-a-quarter in the first semi-final, Federer was on the plane home.

The Simon match saw Djokovic at his most perplexing. He was disorientated and dispirited, before tapping into the beast within him in the final set.

Against Federer, he roared from the start. This was the real Djokovic, the champion roused to near the peak of his powers by a challenger with way more pedigree than the Frenchman but whose gifts were neutered in a whirlwind start.

If Djokovic is to lose his title here on Sunday, he will have to revert to the shadow of himself that nearly lost to Simon. That won’t happen. He can be tested early in a slam but it takes someone special to do it at the end.

Federer failed two years in a row at Wimbledon; Stan Wawrinka pulled it off spectacularly last year at Roland Garros, to deny Djokovic at run at a calendar slam.

This year, he will start favourite in every match he plays and, barring illness or injury, is better placed than at any time in his career to win all four majors before the end of 2016.

You can tell when Djokovic is at his most dangerous. His stare would drill a hole through a brick wall. And Federer proved to be a rather crumbling wall on Thursday night.

ATP statistics analyst Craig O’Shannessy noted that when Djokovic beat Federer 6-3, 6-4 in the ATP World Tour Finals in London last November, he lost only three points on his second serve. “Mind blowing”, was the Australian’s description of that 84 per cent return.

On Rod Laver Arena on Thursday night, the world No1 was similarly lethal if his first serve did not do the damage, winning 21 of 32 points, at 66%. He went eight for eight in the concluding set. Federer – or nearly anyone else, for that matter – could not possibly handle such sustained pressure, and he cracked. His own winning rate on second serve was a respectable 49%, 21 from 43.

How he tried, though. He served and volleyed 17 times, winning the point 11 times – Djokovic did not follow his serve in once – and he won 22 of 34 visits to the net. But too often he was punished for his daring – or was it desperation?

Djokovic does that to players, even great ones, and who could deny Federer’s greatness?

There was a look of resignation on his face from midway through the first half, as Djokovic hit a level as far removed from his struggle against Simon as Mars is from Earth. Indeed, he played tennis from another planet.

It took Federer an hour and 12 minutes to fashion his first break point, but he could not convert it. Within a minute, Djokovic handed him two more opportunities. Ditto. He then pulled off an astonishing serve and chipped a cross-court winner for a fourth break opportunity – not dissimilar to a shot Djokovic had played maybe 20 minutes earlier. This time he completed the execution, forcing his opponent to hit long and he led 4-2.

Winners he missed in the first sets were now landing. He held for 5-2. He served for the set at 5-3. He had set point. Twice. And finally he got on the board.

They closed the roof. Battle resumed. Then numbers went into the crunchers.

ESPN asked viewers if Federer could come back from two sets down to win, and 39% said he could. He has done it nine times in his career, after all.

But this is Djokovic’s time. He only loses when he dips, as Murray observed before the tournament. Federer was reluctant to agree, and said that, unlike Murray, he had done nothing special in his preparation for a match against him.

More numbers: only one player of the 154 who have tried – the Austrian Thomas Melzer in the 2010 French Open – has beaten Djokovic from two sets down in a slam. That is a staggering stat.

Since the start of the US Open, he is 36-1 win-loss, and 16-1 against top 10 players. That, too, is hugely impressive. This is a man at the very peak of his powers, yet with fault lines – and for an hour or so, either side of the roof closure, Federer knew where to probe. Then the beast came back.

There was a tussle in the fourth – and another highlights-reel winner in the penultimate game – but there was also a growing sense of the inevitable. There always is. Even when his level does not stay red-lining at the maximum, Djokovic is still too good for everybody else – including Federer.

Another stat: Federer has never lost a final here. Maybe he never will.

(Guardian service)