Worker encountered me coming up first (5)
I believe the answer is:
emmet
'worker' is the definition.
(I've seen this before)
'encountered me coming up first' is the wordplay.
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'coming up' shows that the letters should be reversed in order (in a down clue, letters go up).
'first' is a charade indicator (letters next to each other).
'me' written backwards gives 'em'.
'met' put after 'em' is 'EMMET'.
(Other definitions for emmet that I've seen before include "someone doing the Eden Project?" , "Hill-dweller" , "Cartoonist" , "tourist in the South West" , "tourist in Cornwall" .)