How tennis ace could be described in decisive moment (5,2,2,6)

I believe the answer is:

point of no return

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'moment' is the definition.
(I have seen 'Crucial moment' mean 'point of no return' so perhaps 'moment' could also mean 'point of no return')

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for point of no return that I've seen before include "Crucial moment" , "ace played?" , "After which one can't go back" , "after which one's committed?" .)

I've seen this clue in The Times.

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