Alexander Zverev fires back with two huge serves as we arrive at the business end of this tie-break with the German 5-4 up.

Carlos Alcaraz can't consolidate his advantage, missing a forehand to go into the change of ends level at three points apiece.

But a timely first serve ensures he edges back in front.

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

This match has been bonkers, hasn't it?

Carlos Alcaraz is using his legs better. He's driving more into the groundstrokes. He's even bouncing.

Zverev looks tight. He hasn't been able to take advantage of what's going on at the other end.

Carlos Alcaraz pounces on a second serve to strike back, before Alexander Zverev nets a backhand to hand Alcaraz the initiative with serve at 3-2.

Alexander Zverev begins the tie-break with an ace and then forces the first mini-break by anticipating a drop shot and adding the finishing touch.

This is a much more level contest now and it does appear as though Carlos Alcaraz is getting back some way towards full health.

The world number one holds to send us into another tie-break after four hours on Rod Laver Arena!

Are we set for a third tie-break in a row, or will Alexander Zverev force a decider with a late break in the fourth set?

Unlike in his previous game, Carlos Alcaraz makes a solid start by winning his first two points.

Jonathan Jurejko
BBC Sport tennis news reporter in Melbourne

Alcaraz is taking care of his serve but barely moving in the returning games.

Can he muster some energy now to earn what would potentially be a match-winning break?

Nope. Another comfortable hold for Zverev, who has only dropped six points on serve in this fourth set.

Image source, Getty Images

Carlos Alcaraz misses a good opportunity as he sends a forehand wide of the mark, but he scoops in a drop shot to get up and running at 30-15.

He hasn't really been able to trouble Alexander Zverev's serve since his cramping issues began, and he's getting more frustrated with his misses than his physical issues now.

Another missed forehand allows Zverev to escape.

Image source, Getty Images

Carlos Alcaraz recovers to 30-30 as Alexander Zverev completely misjudges a return, and then reaches game point as he diverts a forehand into the back corner of Zverev's court.

Another forehand winner is sent fizzing past Zverev and the crowd respond as Alcaraz points to his ear in celebration.

He just refuses to give in.

Serving to stay in the fourth set, Carlos Alcaraz double-faults.

A forehand then flies long to leave Alexander Zverev within two points of the set.

Huge couple of points coming up now in this match...

Carlos Alcaraz just can't get close to Alexander Zverev's serve at the moment, the German smashing in a couple of aces to take his match tally to 15 - and, more importantly, one game from forcing a fifth set.

Image source, Reuters

Carlos Alcaraz beats Alexander Zverev with a trademark drop shot, drawing even louder cheers of encouragement from the stands.

The Spaniard, twice two points from victory in the third set, is back within two games of a place in the final.

Carlos Alcaraz, with cramping legs but new balls to serve with, makes a couple of misses to hand Alexander Zverev 0-30.

It's a strange atmosphere inside Rod Laver Arena right now, but the reactions from the crowd tell you they're trying their best to help Alcaraz back to his best levels.

Still fighting his body, Alcaraz battles back to 30-30 and then drives a backhand down the line for game point.

Jonathan Jurejko
BBC Sport tennis news reporter in Melbourne

Looks like the pickle juice has kicked in.

The acidic liquid is a concentrated source of electrolytes, containing sodium and potassium. It has been found to stop cramping 40% faster than drinking water.

Apparently, pickle juice works by disrupting 'neural signalling' - triggering a reflex in the mouth which sends a signal to stop muscles from cramping.

Judging by the pep which returned to Alcaraz's step in the sixth game, it has worked.

Alexander Zverev makes light work of his latest service game, holding to 15 in the blink of an eye.

Jonathan Jurejko
BBC Sport tennis news reporter in Melbourne

Image source, Getty Images

What's even worse than my Spanish? My German. And that's shameful considering my grandmother was from Bremen.

Anyway... it didn't take any linguistic skills - never mind be a native speaker - to know Zverev was FURIOUS about Alcaraz being allowed that medical timeout.

Grand Slam rules say players are not allowed a medical timeout for cramping.

That was a point being forcefully made by Zverev to the match supervisor in their native tongue.

Whatever happens from here on in, the German third seed will no doubt tee off about the incident in his post-match news conference.

Image source, Getty Images

An ace saves break point number one. A forehand out of Alexander Zverev's reach saves the second.

And even with his physical issues, Alcaraz makes it four points on the bounce to level again.

The Spanish fans are making their appreciation for this effort known!

Carlos Alcaraz's resurgence threatens to hit the buffers as he nets a forehand to present Alexander Zverev with two break points.

Image source, Getty Images

A couple of big serves put Alexander Zverev on track, but Carlos Alcaraz whips in a sensational forehand which scorches the line for 30-30.

Oh, that's a big chance missed! Alcaraz fails to set up a break point as he overhits a forehand on the run, and Zverev gets away to safety.