Was first in the field of racing (3)

I believe the answer is:

led

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'was first' is the definition.
(to lead is to go first)

I can't explain the rest of the clue.

(Other definitions for led that I've seen before include "had the edge" , "Conducted" , "Came first" , "Went in advance of others" , "Went first to show the way" .)

I've seen this clue in the Evening Standard.

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