I have a question regarding the upcoming Australian Open Tournament. Right now there are 59 valid signups, so it is possible that more will come and it will be more than 64. Whats happens then? I suppose that the 64 best ranked players that sign up will get their spot no matter what. But what happens when there are 5 spaces left an 20 unranked players have already signed up? What decides who is allowed to play? First come - first served? Or is it completely by chance? Or can even ranked players not signup for a tournament where enough players have already signed up?
I have not found an answer to this question yet, so I hope that you can help me here

Thanks in advance!