Rose’s part in Sophocles’s Antigone finally overcoming friend (5)
I believe the answer is:
sepal
'rose's part' is the definition.
(sepal is a part of a flower)
'sophocles's antigone finally overcoming friend' is the wordplay.
'finally' indicates one should take the final letters.
'overcoming' means one lot of letters go next to another (some letters are written over others).
'friend' becomes 'pal' (pal is a kind of friend).
The final letters of 'sophocles antigone' are 'se'.
'se'+'pal'='SEPAL'
'in' acts as a link.
(Other definitions for sepal that I've seen before include "bit of a bloomer" , "Enclosing part of flower" , "Violet" , "Part of a flower - peals (anag)" , "Calyx segment" .)