Slag off essentially fine first goal, overturned in loss of cohesion (14)

'cohesion' is the definition.
The definition and answer can be both states of affairs as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'slag off essentially fine first goal overturned in loss of' is the wordplay.
I cannot quite understand how this works, but
'first' could be 'i' (Roman numeral for one or first) and 'i' is present in the answer.
'in' is within the answer.
'of' could be 'o' and 'o' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?