I was first up in food store (4)
I believe the answer is:
deli
'food store' is the definition.
(short for delicatessen)
'i was first up' is the wordplay.
'was first' becomes 'led' (to lead is to go first).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'i'+'led'='iled'
'iled' backwards is 'DELI'.
'in' acts as a link.
(Other definitions for deli that I've seen before include "Exotic food shop" , "Food store" , "food-store?" , "part of supermarket" , "food outlet" .)