Obvious upset originally about opening piece (8)

I believe the answer is:

overture

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'piece' is the definition.
(I've seen this before)

'obvious upset originally about opening' is the wordplay.
'obvious' becomes 'overt' (similar in meaning).
'upset originally about opening' becomes 'ure' (I can't justify this - if you can you should believe this answer much more).
'overt'+'ure'='OVERTURE'

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(Other definitions for overture that I've seen before include "Music played before an opera" , "Musical prelude to opera or ballet" , "used in attempt to seduce?" , "Orchestral work" , "Item of music" .)

I've seen this clue in The Daily Express.

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