Marketing wickedness has secured a win (7)
I believe the answer is:
prevail
'win' is the definition.
(prevailing is a kind of winning)
'marketing wickedness has secured a' is the wordplay.
'marketing' becomes 'pr' (abbreviation for public relations).
'wickedness' becomes 'evil' (synonyms).
'has secured' means one lot of letters goes inside another.
'evil' going around 'a' is 'evail'.
'pr'+'evail'='PREVAIL'
(Other definitions for prevail that I've seen before include "Be current" , "come out on top" , "Be victorious" , "Triumph, overcome" , "Prove more powerful" .)