A chief is leading (5)

I believe the answer is:

ahead

'is leading' is the definition.
(to lead is to go ahead)

'a chief' is the wordplay.
'chief' becomes 'head' (synonyms).
'a'+'head'='AHEAD'

(Other definitions for ahead that I've seen before include "In the leading position" , "advanced" , "Forward - in front" , "Winning" , "at pole" .)

I've seen this clue in The Mirror.

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