Stefanos Tsitsipas will play Dominic Thiem for the title at the ATP Finals after beating six-time champion Roger Federer in London.

The Greek, making his debut at the event aged just 21, won 6-3 6-4.

38-year-old Federer was aiming for a record-extending seventh title but was undone by the nerveless Tsitsipas, just as he was at January’s Australian Open.