Novak Djokovic was again made to fight hard as he beat American wildcard Jenson Brooksby to reach the US Open quarter-finals and keep his calendar Grand Slam hopes alive.

The world number one overcame a poor first set to win a bruising encounter 1-6 6-3 6-2 6-2.

He was pushed all the way by Brooksby, who was well-supported by the full crowd on Arthur Ashe Stadium.

Djokovic will face Matteo Berrettini for a place in the semi-finals.

Djokovic is three wins away from his 21st Grand Slam title, which would be a men's record.