Crossword Genius

The person declared to have won (3)

Ross

I believe the answer is:

one

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'won' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Maybe there's a link between them I don't understand?

I don't understand the rest of the clue.

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(Other definitions for one that I've seen before include "Figure" , "doesn't count for much" , "Hour after midnight" , "If upper-class, perhaps I" , "This is singular" .)

I've seen this clue in the Evening Standard.
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