Postpublished at 13:23 Greenwich Mean Time 24 January
Zverev slips as he sends in a return and that allows Alcaraz to do the rest for 4-2 and daylight.
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 13:23 Greenwich Mean Time 24 January
Postpublished at 13:23 Greenwich Mean Time 24 January
And another! A dream passing shot from Alcaraz with Zverev at the net, 3-2 Alcaraz after taking both points on the German's serve.
Postpublished at 13:22 Greenwich Mean Time 24 January
Image source, Getty ImagesWhat a passing shot from Alcaraz from the baseline, 2-2. Zverev's slight advantage goes.
Postpublished at 13:21 Greenwich Mean Time 24 January
But Alcaraz quickly takes the next point, 2-1 Zverev, who now has two serves.
Postpublished at 13:21 Greenwich Mean Time 24 January
A 22-shot rally, Alcaraz tries to step up the pace, Zverev keeps the point alive and Alcaraz just misses the corner, 2-0 Zverev.
Postpublished at 13:20 Greenwich Mean Time 24 January
Alcaraz tries a soft drop shot, Zverev slips, but the ball doesn't have enough pace to make it over and Zverev takes an early advantage, 1-0 Zverev.
Postpublished at 13:19 Greenwich Mean Time 24 January
A huge cheer from the fans as Alcaraz holds to 15. Zverev, two points away from victory on his own serve not too long ago, has been dragged into a tie-break.
Postpublished at 13:17 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-5 Alcaraz*
Image source, Getty ImagesAlcaraz fires a close-range forehand into the net, 15-15.
'Zverev up against incredible force Alcaraz'published at 13:16 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-5 Alcaraz*
Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra and BBC SoundsAlexander Zverev is up against this incredible force down the other end, the hurricane from Spain.
Carlos Alcaraz no doubt has this belief that he can claw his way back.
Postpublished at 13:15 Greenwich Mean Time 24 January
Zverev 6-1 6-3 6-5 Alcaraz*
Zverev holds to 15 to slam the pressure back on to Alcaraz.
Alcaraz has just broken the Zverev serve to save the match, now he needs to hold his own serve to save the match and force a third set tie-break.
Postpublished at 13:14 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 5-5 Alcaraz
We're at the two-hour mark and what a two hours of tennis this has been.
Postpublished at 13:12 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 5-5 Alcaraz
Image source, Getty ImagesAlcaraz, sliding up to the net, finds a tight angle to somehow flick over a winner and that's for 5-5 in the third set.
How will Zverev react to finally being put under some pressure?
This could still be hugely dramatic.
Postpublished at 13:11 Greenwich Mean Time 24 January
Jonathan Jurejko
BBC Sport in MelbourneRod Laver Arena has just celebrated like Jude Bellingham has scored a last-minute winner at the Bernabeu.
Carlos Alcaraz certainly showed 'cabeza, corazon and cojones' to take his first break point of the match.
Still a long way to go for the Spaniard, but that's the start he had to make.
Now to hold serve...
'Zverev anxious'published at 13:10 Greenwich Mean Time 24 January
Zverev 6-1 6-3 5-4 Alcaraz*
Russell Fuller
Tennis correspondent on BBC Radio 5 Sports Extra and BBC Sounds
Image source, Getty ImagesWhen he lost that service game, Alexander Zverev immediately looked over his shoulder towards his dad, who's also his coach, and those in the box. It was anxiety. He was in searching of reassurance.
Alcaraz breaks back to keep the match alivepublished at 13:05 Greenwich Mean Time 24 January
Zverev 6-1 6-3 5-4 Alcaraz*
Image source, Getty ImagesA massive smile on the Alcaraz face as, at the net, he is able to quickly adjust and flick over a winner.
Zverev, who was once two points away from winning the US Open title, was only two points away from eliminating the second seed and moving into the Australian Open semi-finals.
Alcaraz gets it back on serve. Great drama. The crowd are loving it as we move into Thursday local time.
Postpublished at 13:05 Greenwich Mean Time 24 January
Zverev storms to the net, Alcaraz tries to send it down the line, Zverev can only dump the volley into the bottom of the net. Break point Alcaraz, only his third of the match.
Postpublished at 13:04 Greenwich Mean Time 24 January
Image source, Getty ImagesA 214km/h ace for Zverev makes it 15-30, followed by another blistering ace, superbly placed, for 30-30.
Postpublished at 13:03 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 5-3 Alcaraz
Image source, Getty ImagesA cross-court attempt for Zverev hits the net and Alcaraz, at 0-30, has a lifeline.
'Can Zverev stay relaxed?'published at 13:02 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 5-3 Alcaraz
Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra and BBC SoundsCarlos Alcaraz is giving himself a chance here to keep this set alive and now it's up to Alexander Zverev. Let's see if he can keep his shoulders relaxed on serve.
Postpublished at 13:01 Greenwich Mean Time 24 January
*Zverev 6-1 6-3 5-3 Alcaraz
Alcaraz, crouching low, flicks a great backhand winner and does all he can to keep the match alive. But now he has to break Zverev's serve. Now or never for Alcaraz.