Perform better than unfashionable party (5)
I believe the answer is:
outdo
'perform better than' is the definition.
(I've seen this before)
'unfashionable party' is the wordplay.
'unfashionable' becomes 'out' (similar in meaning).
'party' becomes 'do' (do is a kind of party).
'out'+'do'='OUTDO'
(Other definitions for outdo that I've seen before include "Beat" , "going to top?" , "Surpass - overshadow - excel" , "Exceed" , "Eclipse" .)