Novak Djokovic survives scare to keep calendar grand slam bid on track

Novak Djokovic beat Matteo Berrettini in four sets (Frank Franklin II/AP)

Novak Djokovic survived the biggest test so far in his bid for the calendar grand slam by coming from a set down against Matteo Berrettini to reach the US Open semi-final.

The world number one, looking to add the Flushing Meadows title to his Australian Open, French Open and Wimbledon crowns, dropped the opening set to big-serving sixth seed Berrettini.