Work at opening port (8)
I believe the answer is:
plymouth
'port' is the definition.
(port in Devon)
'work at opening' is the wordplay.
'work at' becomes 'ply' (I've seen this before).
'opening' becomes 'mouth' (mouth is a kind of opening).
'ply'+'mouth'='PLYMOUTH'
(Other definitions for plymouth that I've seen before include "The Pilgrim Fathers landed in USA on . . . Rock" , "Port of which Sir Francis Drake was once mayor" , "where sailors found" , "Mayflower departure, arrival port" , "Laughter my ploy (anag)" .)