World number one Novak Djokovic took a big step towards the semi-finals at the ATP Finals with a clinical victory over Alexander Zverev.
After a very physical and close first set, the Serb ran away with the second to win 6-4 6-1.
Djokovic, chasing a first ATP Finals title since 2015, will reach the last four if John Isner beats Marin Cilic later on Wednesday.
"I don't think it was breathtaking tennis but a win is a win," he said.
More to follow.