Winning with Neath or Garryowen? (2-3-5)

I believe the answer is:

up-and-under

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'garryowen?' is the definition.
I can't tell whether this defines the answer.

'winning with neath' is the wordplay.
'winning' becomes 'up' (eg being up at half time in football).
'with' becomes 'and'.
'neath' becomes 'under' (I can't justify this - if you can you should give a lot more credence to this answer).
'up'+'and'+'under'='UP-AND-UNDER'

'or' acts as a link.

Can you help me to learn more?

I've seen this clue in The Times.

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