Debutant Stefanos Tsitsipas crushed defending champion Alexander Zverev 6-3, 6-2 on Wednesday to book his place in the last four of the ATP Finals with a match to spare.

The 21-year-old, the first Greek player to qualify for the elite eight-man season-ending tournament, backed up his opening round-robin win over Daniil Medvedev with another virtuoso performance at O2 Arena.

His emphatic victory secured a top-two place in the group and left Zverev, world No. 1 Rafael Nadal and Medvedev scrapping to join him in Saturday's semifinals.