Blows away chaff but is first about now (7)

I believe the answer is:

winnows

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'blows away chaff' is the definition.
Although both the answer and definition are verbs in their -s form, I can't see how one could define the other.

'first about now' is the wordplay.
'first' becomes 'wins' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' means one lot of letters goes inside another.
'wins' placed around 'now' is 'WINNOWS'.

'but is' is the link.

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I've seen this clue in the Sydney Morning Herald.

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