Zoo attendant after opening as porter (10)
I believe the answer is:
gatekeeper
'porter' is the definition.
(I know that porter can be written as gatekeeper)
'zoo attendant after opening' is the wordplay.
'zoo attendant' becomes 'keeper' (I've seen this before).
'after' is a charade indicator (letters next to each other).
'opening' becomes 'gate' (a gate is an opening or entrance).
'keeper' after 'gate' is 'GATEKEEPER'.
'as' is the link.
(Other definitions for gatekeeper that I've seen before include "Entry attendant; butterfly" , "man at wicket" , "Entrance attendant" .)