Alexander Zverev downed Novak Djokovic in a thrilling last-four clash to end the world number one's bid for a record-equalling sixth ATP Finals title on Saturday and set up a final against Daniil Medvedev.

The German edged to a 7-6 (7/4), 4-6, 6-3 success in Turin and will face reigning champion Medvedev, who beat Casper Ruud in the other semi, for the trophy on Sunday.

It was a disappointing end to a remarkable season for Djokovic, who fell one match short of becoming the first man to win a calendar Grand Slam since 1969 when he lost the US Open final to Medvedev.

The 20-time major champion was hoping to draw level with Roger Federer on six season-ending championship titles this week in Italy.

But Zverev, who also beat the 34-year-old in the Olympics semi-finals in Tokyo, proved to be a bridge too far for Djokovic again. (AFP)