Alexander Zverev's excellent start continues and he has made nine of 10 first serves and a lovely angled cross-court backhand winner helps him take the game and sprint into a 3-0 lead.

A dream start for Zverev as he breaks the Alcaraz serve at the first time of asking. A sweeping forehand forces the Spaniard wide and he can only net for an early advantage for the German.

Russell Fuller
Tennis correspondent on BBC Radio 5 Sports Extra and BBC Sounds

Carlos Alcaraz has looked increasingly good in the last couple of rounds and certainly against Miomir Kecmanovic in the fourth round, where he recorded a bagel in the fourth set.

Alcaraz is moving through the gears very, very nicely as he tries to reach a first Australian Open semi-final.

Carlos Alcaraz produces a double fault in his first serves of the night and then sends a two-handed backhand into the net to give Zverev an early half chance, 0-30.

Alexander Zverev gets us going and starts off with a hold to 15, finishing off with a close-range volley at the net for an early game in the bag.

Jonathan Jurejko
BBC Sport in Melbourne

A little earlier, Carlos Alcaraz was bopping around to whatever was playing in his earbuds while he limbered up in the players' gym at Melbourne Park.

Bad Bunny, no doubt.

Alcaraz will be hoping to have more pep in his step than Alexander Zverev on Rod Laver Arena tonight.

The Spaniard has breezed through the draw so far, dropping just one set, and has spent eight hours 42 minutes on court over those four matches.

In contrast, Zverev has over five hours of extra running in his legs.

He has spent 13 hours 47 minutes on court this fortnight - including over four hours to beat Britain's Cam Norrie in his previous match.

Alexander Zverev holds a record of two wins and 14 losses at Grand Slams against opponents ranked in the ATP’s top 10.

But a win today would take him into a seventh men’s singles semi-final at a Grand Slam and would move him above Michael Stich's total. Zverev would then only trail Boris Becker (18) for the most among German players in the Open Era.

Image source, Getty Images

Alexander Zverev holds a win-loss record of 4-3 against Carlos Alcaraz.

They have met twice in Grand Slam events, winning one apiece. Zverev won in four sets in their French Open quarter-final in 2022, before Alcaraz claimed a straight-set win in the quarter-finals of last year's US Open.

At 20 years and 262 days, Alcaraz is the fourth-youngest player in the Open Era to reach the men’s singles quarter-final at each of the four Grand Slam events - older only than Boris Becker, Rafael Nadal and Novak Djokovic.

Jonathan Jurejko
BBC Sport in Melbourne

If you aren't fortunate enough to have a ticket for Rod Laver Arena tonight, this is probably the next best spot.

The Grand Slam Oval at Melbourne Park - packed with gigantic television screens, comfy lounging chairs, swanky bar terraces sponsored by premium booze brands and a DJ booth - does not feel like a tennis tournament.

It feels more like a hip night spot on the River Yarra or down by the beach in St Kilda.

During the middle weekend, especially when the sun is blazing, it could be mistaken for Ibiza.

A little calmer tonight.

Image source, BBC Sport

Image source, BBC Sport

Image source, BBC Sport

Chanda Rubin
American former world number six on BBC Radio 5 Sports Extra and BBC Sounds

Image source, Getty Images

That was the best tennis Qinwen Zheng has played all tournament long.

For players, you can have what seems like a low moment. For Zheng, it was losing a coaching relationship that she was committed too, that she thought she was going to build with, that she thought was paying dividends and she was having success with.

A few months later, you can have your highest moment and you will never know it's right around the corner. You've just got to stay the course, make good decisions and stay positive.

Image source, Rex Features

Carlos Alcaraz reached the third round of the Australian Open in 2022, but a leg injury meant he missed out on Melbourne in 2023.

"It feels better to make the quarter-final here in Melbourne," said the 20-year Spaniard. "It's a really big tournament, an amazing tournament. I'm proud with the level I'm playing. It's going to be a really tough quarter-final against Sascha [Zverev].

"I'm feeling better and better every day and every match I'm playing. I'm coming into the quarter-final with a lot of confidence and will try to take this as an advantage.

"He's a really great player and has beaten great guys here in this tournament. Obviously I love playing against him. It's always a tough battle and I have to play my best level. He pushes me to play my 100% every time.

"The last time we faced each other [in the 2023 ATP Tour Finals], I lost so I have to focus on that and improve my level from that match. I'm going to enjoy it and I think for the crowd it's going to be a great match, as well."

This is the first time in the Open Era where each of the top six seeds have reached the men’s singles quarter-finals at the Australian Open.

If Alcaraz wins it means the top four seeds will be the four semi-finalists with the winner of this one against third seed Daniil Medvedev, with top seed Novak Djokovic facing fourth seed Jannik Sinner in the other semi-final.

Jonathan Jurejko
BBC Sport in Melbourne

On the way into Rod Laver Arena, there is a LED screen bearing the slogan 'AO Finals hit different'.

Carlos Alcaraz's face features alongside six others - including Novak Djokovic and Coco Gauff - who could be playing on the last weekend of this year's tournament.

At first I though there was no room for Alexander Zverev. Then I realised he appears on the other side of the advertisement.

Sure somebody is primed to digitally wipe out Linda Noskova, Hubert Hurkacz, Anna Kalinskaya and Alcaraz/Zverev a little later on.

Image source, BBC Sport

Image source, BBC Sport

Image source, Reuters

Two of Alexander Zverev's four matches at this year's Australian Open have gone five sets, while Carlos Alcaraz has only dropped one set so far.

But Zverev said he does not feel like he did in last year's US Open quarter-final loss to Alcaraz, which came two days after Zverev had played a five-setter against Jannik Sinner.

"If you play less, you are fresher, but I feel OK," said Zverev after his five-set triumph over Britain's Cameron Norrie on Monday. "I'm not like the US Open where I was completely dead and where I feel like I'm physically exhausted.

"I'm tired, for sure, because I played 7-6 in the fifth set again two times out of the last three matches, but I'm not dead. I'm not completely exhausted. I'm not in the same physical state I was in the US Open. I expect it to be very different, to be honest.

"Coming out on the Rod Laver Arena for a quarter-final match against the number two player in the world, that gives you energy, as well. I hope it's going to be a very fun, entertaining match."

In the men's draw, we already know that defending champion Novak Djokovic will meet Jannik Sinner for a place in the final.

But who is going to play Daniil Medevdev, after the Russian's 7-6 (7-4) 2-6 6-3 5-7 6-4 win over Hubert Hurkacz earlier today?

Next up on Rod Laver Arena, it's Carlos Alcaraz against Alexander Zverev to complete the semi-final line-ups.

Excited? You should be.

Image source, Getty Images

Here's what China's Qinwen Zheng had to say after beating Russia's Anna Kalinskaya to reach the Australian Open semi-finals:

"Anna Kalinskaya played really good today. She's got really good baseline strokes. In the first set, we had a big competition. The match was really tough for me and I just told myself stay focused and don't think anymore about the first set.

"I'm so happy right now and really excited. I'm really happy to be in the semi-finals especially with such a good performance like this."

On reaching the top 10 for the first time, she added:

"Thanks for letting me know that. Nobody told me anything! That's good news for me. Another motivation. Especially since last year at the Australian Open I said I want to be top 10 and one year later, I'm here. It's an amazing moment."

So, here are your women's semi-finals at the Australian Open 2024:

[2] Aryna Sabalenka v Coco Gauff [4]

[12] Zheng Qinwen v Dayana Yastremska

Who is your winner?

A top effort by world number 75 Anna Kalinskaya but, perhaps hampered by a slight injury issue, she could not live with Zheng Qinwen in that final set.

Having reached her first major quarter-final at the US Open, Zheng will now enter the world's top 10 following the tournament.

She'll face world number 93 Dayana Yastremska for a place in the final.

Zheng, with a four-game cushion and able to hit freely now, unleashes a forehand down the line for 15-15.

A tired forehand from Kalinskaya misses and it feels as though there's not long left in this now.