That should come as no surprise, given the way Djokovic gets into back-and-forths with hecklers at his matches—including Friday night at Rod Laver Arena.

The 10-time title winner at Melbourne Park moved into the fourth round with his most confident performance of the week, a 6-1, 6-4, 6-4 victory over the 26th-seeded Tomas Machac.

Count Novak Djokovic as being in Danielle Collins’ corner. He thinks her response to booing fans at the Australian Open was ...