Door of opportunity? (7)
I believe the answer is:
opening
This clue is a double definition.
'door' is the first definition.
(thesaurus)
'opportunity?' is the second definition.
(I know that opening is a type of chance)
'of' is the link.
(Other definitions for opening that I've seen before include "Aperture or first night" , "Job opportunity" , "Rent" , "Initial" , "launch" .)