AUSTRALIAN OPEN ’19: Djokovic, Federer each eye title No. 7

              FILE - In this Wednesday, Nov. 14, 2018, file photo, Novak Djokovic of Serbia celebrates after defeating Alexander Zverev of Germany in the ATP World Tour Finals men's singles tennis match at O2 arena in London. Djokovic is one of the men to keep an eye on at the Australian Open, Jan. 14-27, 2019. (AP Photo/Alastair Grant, File)

Men to watch at the Australian Open, where play begins Monday: