Party friend keeping in control (8)
I believe the answer is:
dominate
'control' is the definition.
(dominating is a kind of controlling)
'party friend keeping in' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'friend' becomes 'mate' (mate is a kind of friend).
'keeping' means one lot of letters goes inside another.
'mate' enclosing 'in' is 'minate'.
'do'+'minate'='DOMINATE'
(Other definitions for dominate that I've seen before include "Admit one in order to be in control" , "Master" , "Rule" , "Command, control" , "corner" .)