Master wrestling holds in advance (7)
I believe the answer is:
supremo
'master' is the definition.
'wrestling holds in advance' is the wordplay.
'wrestling' becomes 'sumo' (I've seen this before).
'holds' is an insertion indicator.
'in advance' becomes 'pre' (prefix meaning 'before').
'sumo' enclosing 'pre' is 'SUPREMO'.
(Other definitions for supremo that I've seen before include "Person in overall charge, top banana" , "Overall head" , "Person in overall charge, big boss" , "One in overall charge" , "Champion" .)