Postpublished at 12:24 Greenwich Mean Time 24 January
Zverev 6-1 5-3 Alcaraz*
Alcaraz misjudges a forehand from deep, sending it too long and that's 30-30, Zverev two points away from collecting the set.
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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
Michael Emons, Harry Poole and Adam Chowdhury
Zverev 6-1 5-3 Alcaraz*
Alcaraz misjudges a forehand from deep, sending it too long and that's 30-30, Zverev two points away from collecting the set.
Zverev 6-1 5-3 Alcaraz*
A hold to love for Zverev as a running Alcaraz can only flick a shot long and that takes Zverev one game away from a two-set advantage.
*Zverev 6-1 4-3 Alcaraz
Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra and BBC Sounds
I'm loving it with everybody else that is here watching it on Rod Laver Arena.
Those in the Carlos Alcaraz camp are probably a little agitated but they would have to acknowledge the high level of Alexander Zverev.
*Zverev 6-1 4-3 Alcaraz
We mentioned earlier on Alcaraz was taking his time over his serves and this time he gets a time violation warning as the clock runs out.
That was on break point down but the delay doesn't put off Zverev and he gets a break.
In a match of superb quality, Zverev finds himself a set and a break up.
Zverev 6-1 3-3 Alcaraz*
Gigi Salmon
BBC Sport tennis commentator on BBC Radio 5 Sports Extra and BBC Sounds
What we are witnessing is off the charts! This is silly tennis.
Jonathan Jurejko
BBC Sport in Melbourne
Talk about contrasting expressions.
Zverev, face fuming and hands on hips, cannot believe that backhand return at deuce went wide.
Alcaraz grins that wide grin - mainly in relief - as the replay shows close it was.
But the Spaniard isn't laughing when another chance comes Zverev's way after a breath-taking point.
Zverev 6-1 3-3 Alcaraz*
What a point, with Zverev three times volleying at the net what look to be winners, but Alcaraz keeps two of those points alive but, sliding and stretching, he can't do it again.
Break point for Zverev.
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This is a tasty encounter, having watched these two battle it out live at Turin, I've got a feeling that we're in for a gruelling five-set battle.
Dr Daud Khan
Zverev 6-1 3-3 Alcaraz*
A beautiful forehand winner straight down the line from Zverev and that means it's 11 winners each.
That was for 15-30, and Alcaraz later sees a drop shot from deep come up short and we're at deuce in game seven of set number two.
Zverev 6-1 3-3 Alcaraz*
Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra and BBC Sounds
That game was pretty decent. It's building. The crowd want to see the tussle and are pro-Carlos Alcaraz at the moment. Alexander Zverev was able to fight and serve his way out of trouble there.
Zverev 6-1 3-3 Alcaraz*
That's an impressive hold from Zverev, who has to fend off two break points. Not this time for Alcaraz.
*Zverev 6-1 2-3 Alcaraz
A two-handed backhand from Alcaraz nets and that was on the second of two break points and we're at deuce.
*Zverev 6-1 2-3 Alcaraz
Jonathan Jurejko
BBC Sport in Melbourne
The real Carlos Alcaraz has arrived.
Forehand returns are firing now, with an increased mph and accuracy, and Zverev suddenly has a problem.
*Zverev 6-1 2-3 Alcaraz
Three stunning forceful forehands in a row from Alcaraz and he's blasting himself through this phase of the match. That gives Alcaraz 15-30 on the Zverev serve. Can the German deal with this onslaught?
*Zverev 6-1 2-3 Alcaraz
Jonathan Jurejko
BBC Sport in Melbourne
It's not often Carlos Alcaraz loses a set 6-1. It's even rarer that it is the first set.
That's only happened once before in his career at tour level.
Anyone remember when? Of course you do.
It was last year's Wimbledon final against Novak Djokovic.
And we all know what happened then...
*Zverev 6-1 2-3 Alcaraz
Some great defence from Zverev in a 17-shot rally, but Alcaraz, always edging closer to the net, is able to stretch and reach a volley and then guide it just inside the line.
Alcaraz ends the fifth game of the second set with an ace and has only dropped one point in his past two service games - and that spells danger for Zverev.
Zverev 6-1 2-2 Alcaraz*
A hold to love for Zverev, with some excellent serving out wide to counter the Alcaraz threat.
*Zverev 6-1 1-2 Alcaraz
Mark Woodforde
17-time Grand Slam doubles champion on BBC Radio 5 Sports Extra and BBC Sounds
For Alexander Zverev, it was probably important to win that first set. For Carlos Alcaraz, no panic and he can make a charge. This set in the next 10 or 15 minutes, I think we'll see a little more from Alcaraz.
*Zverev 6-1 1-2 Alcaraz
Jonathan Jurejko
BBC Sport in Melbourne
The shout of 'Vamos' from Alcaraz which greets the hold has some extra oomph.
He knows the importance of being fired up and alert, just waiting for Zverev's level to drop so he can try to take advantage.
*Zverev 6-1 1-2 Alcaraz
"Vamos", is the cry from Alcaraz as a serve tight into the Zverev body is flicked away and wide for a hold to 15 for Alcaraz, with one of his best service games of the match so far.
After a surprisingly one-sided first set, the second is much, much tighter and it's warming up nicely.