In uncomplicated final part of course (4,8)
I believe the answer is:
home straight
'final part of course' is the definition.
(final part of a racecourse)
'in uncomplicated' is the wordplay.
'in' becomes 'home' ('he's in' can mean 'he's home').
'uncomplicated' becomes 'straight' (straight can mean simple or uncomplicated).
'home'+'straight'='HOME STRAIGHT'
(Other definitions for home straight that I've seen before include "final stage of race" , "Last stage of race" , "Final stage of a racecourse" , "Last part of a race" , "covered in neat report" .)