Serene porter on the counter pockets key (6)
I believe the answer is:
opener
'key' is the definition.
(I've seen this before)
'serene porter on the counter pockets' is the wordplay.
'pockets' indicates a hidden word (pocket can mean to contain).
'the counter' says the letters should be written backwards.
'renepo' is hidden within 'serene porter on'.
'renepo' written backwards gives 'OPENER'.
(Other definitions for opener that I've seen before include "Introductory remark" , "See 1" , "Corkscrew, for example" , "Batsman number one" , "First in batting order" .)