Miserable service begins disappointment (7)

I believe the answer is:

letdown

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'disappointment' is the definition.
(something or someone which lets you down)

'miserable service begins' is the wordplay.
I cannot quite see how this works, but
'miserable' could be 'down' and 'down' is present in the answer.
'service' could be 'let' (type of tennis serve) and 'let' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Independent.

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