Spoke about one number overturning analysis of problem (9)

I believe the answer is:
diagnosis
'analysis of problem' is the definition.
'diagnosis' can be an answer for 'analysis' (I've seen this before). I am not sure about the 'of problem' bit.
'spoke about one number overturning' is the wordplay.
I cannot really understand how this works, but
'about' could be 'a' (abbreviation in Chambers) and 'a' is found within the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'number' could be 'i' (I is an example) and 'i' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for diagnosis that I've seen before include "Interpretation of" , "doctor's opinion" , "medical opinion" , "Identification of a problem from its symptoms" , "analysis" .)
