0-15 becomes 0-30 as Alexander Zverev misses a backhand.

Here we are then.

Alexander Zverev steps up to serve for a place in the Australian Open final.

Carlos Alcaraz punishes his cautious approach on the opening point for 0-15.

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A big chance missed by Alexander Zverev as he hits a forehand long after chasing down a drop shot, which could have brought him to 30-30.

Carlos Alcaraz wriggles free to force Zverev to try and serve this out after five hours and 10 minutes of dizzying drama in Melbourne.

Jonathan Jurejko
BBC Sport tennis news reporter in Melbourne

Alcaraz can't believe it. Neither can anyone else on Rod Laver Arena.

Another golden opportunity slips by the wayside as Alcaraz goes to town on that forehand.

The Spaniard is now 0-5 on break points in this decider. The inability to convert them is increasingly looking like proving the difference.

Zverev off the hook again!

We're less than 10 minutes away from this becoming the longest ever semi-final in Australian Open history as Carlos Alcaraz steps up to serve and try and stay in this match.

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Argh! Frustration for Carlos Alcaraz as he drags a forehand wide.

Alexander Zverev survives again, and then reaches game point as he drives in a forehand at the net.

A stunning winner from the German then gets the love it thoroughly deserves.

If he does come through this, it has to be up there as one of the best wins of his career.

Great resistance once more from Alexander Zverev, seeing off a fourth break point in this set.

But he's going to have to face up to a fifth as Carlos Alcaraz continues to throw absolutely everything at him!

Carlos Alcaraz gets the better of Alexander Zverev at the net.

Another break point for the Spaniard!

Alexander Zverev continues to show impressive concentration in the big points in this decider, recovering to 30-30.

Applause rings around Rod Laver Arena, for both players, as the clock moves past the five-hour mark.

The noise only grows louder as Carlos Alcaraz battles to deuce.

Jonathan Jurejko
BBC Sport tennis news reporter in Melbourne

Everyone knows the forehand is Alexander Zverev's weaker wing.

Its reliability has let him down in some big moments over the years but, blimey, is it standing up to the test now.

Zverev has come under pressure from Alcaraz on that side, but kept his nerve and kept pummelling away in this decider.

Coming through the game point for 4-2 illustrated that in a nutshell.

Alexander Zverev has come through three break points in his past two service games.

But still he remains on course for the final.

A couple of misses gift Carlos Alcaraz 0-30. Now this really is an opening he must take.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra

We went through a long patch of very short points with lots of drop shots thrown in, but now the rallies are starting to extend.

We are just a few minutes short of five hours on court. The legs are going to hurt.

Approaching the five-hour mark, Carlos Alcaraz finds a couple of winners on his way to a 40-0 lead as he seeks to quickly put the pressure back on Alexander Zverev.

Zverev manages to get on the board before Alcaraz wraps it up moments later.

Annabel Croft
Former British number one on BBC Radio 5 Sports Extra

It's interesting to see Alcaraz like this. He has been quite subdued for a lot of the time that he hasn't been 100% physically. It's good to see him try and energise the crowd and try and inject energy into himself.

You know that he is still fired up and I still think there might be another twist in this.

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Carlos Alcaraz can't take his opportunity and, credit to Alexander Zverev, the German keeps his cool under intense pressure to land a winner for game point.

Alcaraz is left with his hands on his knees after producing an effort that seemed beyond his physical capabilities not too long ago.

Zverev once again survives a break point to edge closer to the finish line. The third seed is showing serious grit here.

It is still Alexander Zverev who remains in control for now. But, having come through two break points in his previous game, there are likely more tense moments ahead for the German.

Carlos Alcaraz leaps up into a forehand to stay in touch at 30-15...

And now he has the crowd back on their feet!

He was barely able to walk two hours ago. Now he's sprinting after seemingly lost causes - and rescuing them.

A stunning pick-up at the net brings him to 30-30, and now he'll have break point from 30-0 down! Incredible.

Image source, Getty Images

Carlos Alcaraz misses another chance to close out the game, but he'll get a third attempt after he arrows a forehand down the line to leave Alexander Zverev stranded.

Gets it! A drop shot beats Zverev and Alcaraz waves another fist to the crowd.

He's not going anywhere yet!

A defiant shake of the fist from Carlos Alcaraz follows as he overpowers Alexander Zverev with a hefty forehand into the back of the court.

But he hasn't managed to shake off Zverev just yet. The third seed reaches deuce.

Jonathan Jurejko
BBC Sport tennis news reporter in Melbourne

Here's another belter of a stat... Alcaraz has never lost at a Grand Slam after winning the opening two sets.

According to Tennis Abstract - the bible for facts and figures - Alcaraz has gone on to record victory in each of the 55 matches where he has led by two sets to love.

That record is looking perilous. But you wouldn't dream of ruling him out just yet.

Was that the chance for Carlos Alcaraz?

What is near-certain is that the Spaniard, with all the physical issues he has had to overcome to still be out on the court, cannot afford another setback here.

Alexander Zverev fires in a quite stunning forehand for 15-30.