Novak Djokovic, Coco Gauff roll to Australian Open's 4th round. Naomi Osaka retires due to injury and Jessica Pegula was upset in the third round.

Novak Djokovic has been one of many players who have been heckled at the Australian Open - and the 10-time champion praised Danielle Collins' response to the rowdy crowd

Count Novak Djokovic as being in Danielle Collins’ corner. He thinks her response to booing fans at the Australian Open was absolutely fine — which should come as no surprise, given the way Djokovic gets into back-and-forths with hecklers at his matches,