Perform better than unpopular party (5)
I believe the answer is:
outdo
'perform better than' is the definition.
(I've seen this before)
'unpopular party' is the wordplay.
'unpopular' becomes 'out' ('out' can be similar in meaning to 'unpopular').
'party' becomes 'do' (do is a kind of party).
'out'+'do'='OUTDO'
(Other definitions for outdo that I've seen before include "Perform better than, be superior to" , "Surpass someone at something" , "Exceed" , "going to top?" , "Surpass, go one better than" .)