Why are they playing tennis matches until nearly 4 a.m. at the Australian Open?

A smile creased Daniil Medvedev's face as he walked to the net in Rod Laver Arena at 3:39 a.m., finally a winner in the Australian Open's second round after five sets spread across nearly 4 1/2 hours in the third-latest finish in Grand Slam history. Zero chance Medvedev would have been there at that time if he didn't need to be.