Immediately in a tricky situation (2-3-4)

I believe the answer is:
on-the-spot
'immediately' is the definition.
(I've seen this before)
'tricky situation' is the wordplay.
'tricky' becomes 'onthe' (I can't justify this - if you can you should give a lot more credence to this answer).
'situation' becomes 'spot' (synonyms).
'onthe'+'spot'='ON-THE-SPOT'
'in a' acts as a link.
Can you help me to learn more?
I've seen this clue in The Times.
Want a hint initially instead of a full solution?
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