Alexander Zverev stunned dynamic Spaniard Carlos Alcaraz in the early hours of Thursday to surge into an Australian Open semi-final against Daniil Medvedev, weathering a big fightback from the world number two.

The German sixth seed eventually prevailed 6-1, 6-3, 6-7 (2/7), 6-4 on Rod Laver Arena to make the last four at a Grand Slam for the seventh time.

Zverev, still searching for a breakthrough major title, will meet Medvedev next after the Russian third seed battled past Poland's Hubert Hurkacz in five gruelling sets.

But he had to dig deep to get past Alcaraz, who was 2-5 down in the third set and seemingly out for the count.

"I'm playing one of the best players in the world, especially over the last two years ... he's won two Grand Slams," said Zverev.

"When you're up 6-1, 6-3, 5-2, you start thinking, 'we're all human, and it's a great honour to play against guys like this' and when you're so close to winning your brain starts going and it's not always helpful.

"But I'm happy that I fought back quite well in the fourth set and didn't let go."

The 26-year-old last made the semis in Melbourne in 2020 and has only once been to a Grand Slam final, when he lost the 2020 US Open decider to Dominic Thiem despite holding a 2-0 lead.

Before meeting Zverev, Alcaraz had only dropped one set and a single service game and had spent five hours less on court than the German.

But he did not know what had hit him in the opening set, with an ultra-aggressive Zverev ripping through it in 29 minutes, getting 16 of 18 first serves in play and winning 14 of those points.

The Spaniard refocused and was more authoritative in the second set, hitting his groundstrokes and getting to the net.

But Zverev saved two break points in the sixth game then swooped in the next game, coming to the net for a winner to move 4-3 ahead and breaking again to take the set.

A shellshocked Alcaraz struggled to find a way back, with a double fault gifting the German a third break point, which he converted to pull 3-1 clear in the third set.

Zverev moved 5-2 ahead and it looked all over when he served for the match at 5-4, but the Spaniard flicked a switch and produced some sensational tennis to break for the first time.

It went to a tiebreak and with the crowd roaring him on Alcaraz took it to a fourth set.

Zverev appeared exhausted, but he found another wind and forced errors from Alcaraz for a crucial break and a 5-4 lead in the fourth and this time made no mistake serving for the match.