Carlos Alcaraz won a spellbinding battle of the young guns against Jannik Sinner to reach his first grand slam semi-final in a thriller with the US Open's latest-ever finish.

Spanish teenager Alcaraz finally clinched a 3-6 7-6 (7) 7-6 (0) 5-7 6-3 victory at 2.50am after five hours and 15 minutes of full-throttle tennis to set up a clash with Frances Tiafoe on Friday.

Remarkably, three matches had previously finished at 2.26am, while this was the second time Alcaraz had played beyond 2am in succession after his fourth-round win over Marin Cilic finished at 2.23am.

The 19-year-old saved a match point in the fourth set and came from a break down in the decider against his 21-year-old opponent to show once again what a special talent he is. He could yet leave New York as the world No 1 too.

Sinner's spell as the brightest young talent in tennis was swiftly cut short by the emergence of Alcaraz, who swept past his rival and into the top 10.

But the Italian had come out on top in their two recent meetings, in the fourth round at Wimbledon and then at the ATP tournament in Umag, Croatia.