Consume last of open port (5)
I believe the answer is:
haven
'port' is the definition.
(I have seen 'Safe port ' mean 'haven' so perhaps 'port' could also mean 'haven')
'consume last of open' is the wordplay.
'consume' becomes 'have' ('have' can be a synonym of 'consume').
'last of' indicates one should take the final letters.
The final letter of 'open' is 'n'.
'have'+'n'='HAVEN'
(Other definitions for haven that I've seen before include "Harbour, oasis" , "Anchorage - retreat" , "A peaceful refuge" , "Safe harbour" , "Safe port" .)