Unfair to lose top mechanic (7)
I believe the answer is:
artisan
'mechanic' is the definition.
(I've seen this before)
'unfair to lose top' is the wordplay.
'unfair' becomes 'partisan' (I've seen this before).
'to lose top' means to remove the first letter.
'partisan' with its initial letter taken off is 'ARTISAN'.
(Other definitions for artisan that I've seen before include "Technician" , "Skilled worker by hand" , "Skilled worker or craftsman" , "Tsarina (anag.)" , "Crafty sort" .)