Bartok's first duet sent round for first performance (5)
I believe the answer is:
debut
'first performance' is the definition.
(I've seen this in another clue)
'bartok's first duet sent round' is the wordplay.
'bartok's first' becomes 'b' (1st letter of 'bartok').
'sent' indicates anagramming the letters (send can mean to excite or stimulate).
'round' means one lot of letters goes inside another.
'duet' anagrammed gives 'deut'.
'b' inserted inside 'deut' is 'DEBUT'.
'for' acts as a link.
(Other definitions for debut that I've seen before include "Tubed (anag.)" , "First appearence as of society girl" , "First attempt" , "Beginning, first performance" , "Initial appearance" .)