Carlos Alcaraz advances at Australian Open after Shang Juncheng retires hurt

Remarkably, this was 20-year-old Alcaraz's first experience of playing a younger player in his 201st tour level match, but it was barely a contest, the second seed dropping just two games before Shang called it a day trailing 6-1 6-1 1-0.

The 18-year-old Chinese wild card began the match with heavy strapping on his right thigh and took a medical timeout in the second set.

Alcaraz was forced to miss the tournament last year with a leg injury, and he said: "I was watching the matches at home from the couch, wishing to play in the second week here. It feels special."

The young Spaniard will expect to go further than just the fourth round, where he will play Serbia's Miomir Kecmanovic.

The latter saved two match points for the second round in a row, defeating American Tommy Paul 6-4 3-6 2-6 7-6 (7) 6-0.

One of the biggest surprises of the week so far has been French wild card Arthur Cazaux, who brushed aside 28th seed Tallon Griekspoor 6-3 6-3 6-1 to make the last 16 on his debut.

Ranked 122, the 21-year-old is one of a crop of young players emerging, but far from the most heralded.

He said: "Of course there are so many players much better in the ranking than me, young players like Carlos, Holger (Rune), Jannik (Sinner), and Arthur Fils also. Of course I know them, because we were in juniors together.

"Yes, they are superstars now, so it's crazy for them. Me, I did my trip. I had many injuries, and then I did my best. I do my trip, and we will see where it's going to be."

He will next play ninth seed Hubert Hurkacz, who came from a set down to defeat another Frenchman, Ugo Humbert, 3-6 6-1 7-6 (4) 6-3.

The biggest upset of the day was delivered by Nuno Borges, who knocked out in-form 13th seed Grigor Dimitrov 6-7 (3) 6-4 6-2 7-6 (6) to become the first Portuguese player to make the fourth round in Melbourne.

In the last 16 he will take on third seed Daniil Medvedev, who bounced back from his 3.39am finish against Emil Ruusuvuori on Friday morning to defeat Felix Auger-Aliassime 6-3 6-4 6-3.

The Russian revealed he did not go to bed until 7am, saying: "Physically today was very tough, but I'm happy that I managed to be able to play the match, to play it quite good, serving well.

"I felt like I could be better when moving to the ball. That's normal. My body was not 100 per cent. But I'm happy to be here in two days. I feel like now I have enough time to recover 100 per cent and be ready for the next match."

Sixth seed Alexander Zverev avoided a long night on Laver, seeing off American teenager Alex Michelsen 6-2 7-6 (4) 6-3 to set up a clash with Britain's Cameron Norrie.

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