Postpublished at 14:17 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 6-7 (2-7) 5-4 Alcaraz
A great serve down the middle and, just as he was in set three, Zverev is two points from the semi-finals, 30-15.
Summary
Listen to 5 Sports Extra commentary at top of page (UK only)
NOW: Alexander Zverev beats Carlos Alcaraz 6-1 6-3 6-7 (2-7) 6-4 in men's quarter-finals
German will play Daniil Medvedev, who beat Hubert Hurkacz 7-6 (7-6) 2-6 6-3 5-7 6-4
Qualifier Dayana Yastremska beats Linda Noskova in straight sets to reach first major semi-final
Zheng Qinwen beats Anna Kalinskaya 6-7 (4-7) 6-3 6-1 to reach women's singles semi-finals
Britain's Neal Skupski and American partner Desirae Krawczyk reach mixed doubles final
Postpublished at 14:17 Greenwich Mean Time 24 January
Postpublished at 14:16 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 6-7 (2-7) 5-4 Alcaraz
An excellent baseline rally ends with Alcaraz drawn into an unforced error and he nets for 15-0 to Zverev, three points from victory.
Zverev breaks, serving for a place in the semi-finalspublished at 14:13 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 6-7 (2-7) 5-4 Alcaraz
Image source, Getty ImagesAlcaraz has broken the Zverev serve when being one game away from defeat. Now he has to do the same again after the German gets what could be the decisive break in the ninth game of the fourth set.
Can Zverev finish the job off this time?
Postpublished at 14:13 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-7 (2-7) 4-4 Alcaraz*
We move into a fourth hour.
Postpublished at 14:13 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-7 (2-7) 4-4 Alcaraz*
Two break points for Zverev. This is huge.
Postpublished at 14:13 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-7 (2-7) 4-4 Alcaraz*
"Nooo", calls Alcaraz as the radar is off and he slips a forehand wide. Zverev 15-30 on the Alcaraz serve.
'Zverev showing guts'published at 14:12 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-7 (2-7) 4-4 Alcaraz*
Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra and BBC SoundsAlexander Zverev is showing a lot of guts tonight. It comes on the back of a five-set match with Cameron Norrie.
It wasn't all easy service games against Norrie either. He had to grind it out in four hours plus of play. It's like Zverev has played himself into some form.
Postpublished at 14:12 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-7 (2-7) 4-4 Alcaraz*
Jonathan Jurejko
BBC Sport in Melbourne
Image source, Getty ImagesEven the Spanish fans and journalists on Rod Laver Arena can't help but applaud that game-winning point for Zverev.
Incredible stuff from both players at such an important stage of a tense and tight set.
Postpublished at 14:11 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-7 (2-7) 4-4 Alcaraz*
Zverev has already served for the match once today, a break here and he will be doing so again. This is a huge game coming up.
Postpublished at 14:10 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-7 (2-7) 4-4 Alcaraz*
What a match this is and another sensational rally, full of great, unbelievable shots and with both men thinking they had the edge.
Zverev gets the game thanks to an angled shot that Alcaraz can only send into the net.
get involved Get Involvedpublished at 14:08 Greenwich Mean Time 24 January
Tweet #bbctennis, text 81111 (standard rates apply), WhatsApp 03301231826
Hugh: So impressive from Carlos Alcaraz. But this scheduling from the Australian Open is appalling. It's 1am AEST and I won't be able to stay up any longer to watch it.
Postpublished at 14:07 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 6-7 (2-7) 3-4 Alcaraz
From 40-0 to deuce, Carlos Alcaraz looks to take advantage of an opponent who may be feeling a tiring campaign that has already included two five-set matches.
Postpublished at 14:05 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 6-7 (2-7) 3-4 Alcaraz
We're approaching the business end of the fourth set and the pressure of it is cranking up. Alcaraz is talking to himself after an unsuccessful shot to give Zverev a few game points.
But Zverev is grimacing as he tries to run to the net. Has he sustained an injury or just the effect of tired legs in an already gruelling match?
'Alcaraz growing in confidence'published at 14:04 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 6-7 (2-7) 3-4 Alcaraz
Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra and BBC SoundsRemarkable turnaround from Carlos Alcaraz. It's still advantage Alexander Zverev but Alcaraz seems like he's growing in a bit of confidence and the pressure is certainly on the German's shoulders.
Postpublished at 14:04 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 6-7 (2-7) 3-4 Alcaraz
Jonathan Jurejko
BBC Sport in MelbourneYou know it's 1am when the crowd sing an 'Ooh-Aah' to DJ Otzi.
We've all been there.
Usually in a nightclub or a wedding, but that's what late-night tennis does to you.
Postpublished at 14:01 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 6-7 (2-7) 3-4 Alcaraz
Image source, Getty ImagesAlcaraz has now hit 16 forehand winners and that is a large reason why this match is still going when Zverev was so close to victory.
A serve out wide sees Zverev stretching and sticking the return in the net, as Alcaraz edges back ahead in set four.
'Zverev box not saying anything'published at 13:59 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-7 (2-7) 3-3 Alcaraz*
Gigi Salmon
BBC Sport tennis commentator on BBC Radio 5 Sports Extra and BBC Sounds
Image source, ReutersNo one in the Alexander Zverev box has said a word I think for the entirety of the match. They're just leaning forward, hands together.
Even when Zverev was serving for the match and for a place in the semi-finals, they wouldn't look at each other, they wouldn't talk to each other.
Postpublished at 13:58 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-7 (2-7) 3-3 Alcaraz*
Zverev moves into the net and dispatches a high leaping volley before producing his seventh ace of the night to take us to 3-3 at the halfway point of the fourth set.
'Alcaraz positive'published at 13:56 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 6-7 (2-7) 2-3 Alcaraz
Gigi Salmon
BBC Sport tennis commentator on BBC Radio 5 Sports Extra and BBC SoundsCarlos Alcaraz is a very positive young man. The head didn't drop. There was one outburst earlier on but the smile remained. The positivity remained, the body language on the whole was good.
Postpublished at 13:55 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 6-7 (2-7) 2-3 Alcaraz
Which way will this one go? Although Zverev is two sets to one up, you'd still be brave to bet against Alcaraz turning this one around and advancing.
The Spanish flags are out and being waved with extra excitement now as he nudges back ahead in the fourth set. Daniil Medvedev awaits the winner, but who will that be?