A unique stroke (3)

I believe the answer is:

ace

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'stroke' is the definition.
(I know that ace is a type of service)

'a unique' is the wordplay.
'unique' becomes 'ce' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'ce'='ACE'

Can you help me to learn more?

(Other definitions for ace that I've seen before include "Very good; playing card" , "Tennis serve that the opponent can't reach" , "One in a suit" , "One-spotted card" , "One; A1" .)

I've seen this clue in the Evening Standard.

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