You don't need to disable Automatic save in AutoCAD Preferences, you can leave it ON.
But you need to turn off creating backup copy (file with the name of the currently saved drawing and with .BAK extension) on each save.
How to:
On the command line in AutoCAD for Mac, type ISAVEBAK, hit Return, type 0 (zero), hit Return again. Then ISAVEBAK system variable will be 0 (zero) and creating .BAK files on each save will be disabled preventing from creation of drawing copy with an incremented number appended to its name.
