Opening bars in Spain troublesome (5)
I believe the answer is:
intro
'opening bars' is the definition.
(opening bars of a piece of music)
'in spain troublesome' is the wordplay.
'in' indicates the answer is hidden within the clue.
'INTRO' is hidden in the letters of 'spain troublesome'.
(Other definitions for intro that I've seen before include "Jazz piece" , "Preliminary section (of music) (colloq.)" , "(Short) section before Chapter 1, say" , "Opener" , "Beginning (colloq.)" .)