World No.1 Novak Djokovic has been disqualified from the US Open after hitting a line judge with the ball after a point during his fourth round match against Spain’s Pablo Carreno Busta.

It was a stunning end to Djokovic’s bid for an 18th grand slam title and his 26-0 start to this season.

The Serbian top seed had just lost a game to Carreno Busta, to fall behind 6-5 in the first set.

As he walked to the sideline for the changeover, Djokovic smacked a ball behind him.

The ball hit a female line judge, who dropped to her knees at the back of the court.

After a discussion of several minutes with officials on court, Djokovic walked over to shake hands with Carreno Busta, and the default was announced.