Game pair on high? (3-2)

I believe the answer is:

two-up

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

'pair on high?' is the wordplay.
'pair' becomes 'two' (I've seen this in another clue).
'on' means one lot of letters go next to another.
'high?' becomes 'up' ('up' is associated in meaning with 'high').
'two'+'up'='TWO UP'

Can you help me to learn more?

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

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