32768!
32768 players start at the 1st hole half of them are knocked out, 16384 players play the 2nd hole and do on till only 2 players are left to play the 18th hole and determine the winner!
I don’t think there have ever been a true knockout tournament, I think there such a thing as a true open either, if it’s really open then you would not need to qualify! Or open really does not mean open!
I know you really did not...
32768!