Novak Djokovic, defending US Open 2019 champion, advanced into the fourth round with a straight-set 6/3, 6/4, 6/2, victory. But his explosive rants during and prior to the game left Nick Kyrgios amused, who aimed a sly dig at the 16-time Grand Slam champion for yelling at the crowd at Flushing Meadows and above all threatening a spectator.