So then going to pieces when one is about to win (2,3,4)
I believe the answer is:
on the nose
'win' is the definition.
(I've seen this before)
'so then going to pieces when one is about' is the wordplay.
'going to pieces' indicates an anagram (going to pieces can mean breaking down).
'when' becomes 'one' (I am not sure about this - if you are sure you should believe this answer much more).
'one is about' means one lot of letters goes inside another.
'so'+'then'='sothen'
'sothen' anagrammed gives 'thenos'.
'thenos' going inside 'one' is 'ON THE NOSE'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for on the nose that I've seen before include "To win one" , "where glasses are found?" , "There's a bridge here" , "just to take the first place" , "where might a boxer's punch land?" .)