A terrible blow: pool now feels disturbed (3,4,5)

I believe the answer is:

one fell swoop

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'a terrible blow' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'pool now feels disturbed' is the wordplay.
'disturbed' indicates anagramming the letters (the order of letters is disturbed).
'pool'+'now'+'feels'='poolnowfeels'
'poolnowfeels' is an anagram of 'ONE FELL SWOOP'.

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

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