The World number on Novak Djokovic beat German Alexander Zverev in straight sets 6-4 6-1 this afternoon to become the first man to reach the semi-finals of the ATP Finals in London. This evening Marin Cilic defeated American John Isner 6-7 6-3 6-4. On friday Isner faces Zverev while Cilic will play Djokovic with one other semi-final place at stake.