Spanish teenager Carlos Alcaraz reached his first major semi-final after beating Italy's Jannik Sinner in a US Open thriller which ended at a record latest time of 2.50am in New York.

Alcaraz, 19, saved a match point before clinching an epic 6-3 6-7 (7-9) 6-7 (0-7) 7-5 6-3 win over 11th seed Sinner.

The third seed will face Frances Tiafoe on Friday for a spot in Sunday's final.

The American, 24, also plays in a first major semi-final after his 7-6 (7-3) 7-6 (7-0) 6-4 win over Andrey Rublev.

"I still don't know how I did it. The level I played of high quality tennis. It's unbelievable," said Alcaraz, who is the youngest man to reach a Grand Slam semi-final since Rafael Nadal at the 2005 French Open.

"I always say you have to believe in yourself all the time. Hope is the last thing you use. I believed in myself, my game."

A first-time Grand Slam champion is already guaranteed in the men's singles at Flushing Meadows, with Norway's Casper Ruud and Russia's Karen Khachanov contesting the other semi-final.

Alcaraz and 23-year-old Ruud also have a shot of becoming the new world number one as an intriguing tournament nears a conclusion.