I stumbled upon the weird chrome autofill behaviour today. It happened to enable on fields called: "embed" and "postpassword" (filling there login and password) with no apparent reason. Those fields had already autocomplete set to off.
None of the described methods seemed to work. None of the methods from the another answer worked as well. I came upon my own idea basing on Steele's answer (it might have actually worked, but I require the fixed post data format in my application):
Before the real password, add those two dummy fields:
<input type='text' style='display: none'>
<input type='password' style='display: none'>
Only this one finally disabled autofill altogether for my form.
It's a shame, that disabling such a basic behavior is that hard and hacky.