One manages to do so for oneself (4)

I believe the answer is:

fend

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'one' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?

I cannot understand how the remainder of the clue works.

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(Other definitions for fend that I've seen before include "Manage (usually for oneself)" , "Ward (off); manage (for oneself)" , "Try to manage without help" , "Ward off from offender" .)

I've seen this clue in the Evening Standard.

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