First decision, I emphasised, was upset (10)
I believe the answer is:
distressed
'upset' is the definition.
(I know that upset can be written as distressed)
'first decision i emphasised' is the wordplay.
'first decision' becomes 'd' (1st letter of 'decision').
'emphasised' becomes 'stressed' (similar in meaning).
'd'+'i'+'stressed'='DISTRESSED'
'was' is the link.
(Other definitions for distressed that I've seen before include "in anguish?" , "In deep pain or sorrow" , "Upset; deliberately aged" , "like Samson when deprived of his strength?" , "Anxious" .)