Pop's one to vocalise, daydreaming (11)

I believe the answer is:

fantasising

'daydreaming' is the definition.
(to daydream is to fantasise or imagine)

'pop's one to vocalise' is the wordplay.
'pop's' becomes 'fantas' (fizzy pop).
'one' becomes 'i' (Roman numeral).
'to vocalise' becomes 'sing' (perform vocals).
'fantas'+'i'+'sing'='FANTASISING'

I've seen this clue in The Times.

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