Unexciting partner in an impasse (9)

I believe the answer is:

stalemate

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'an impasse' is the definition.
('stalemate' can be a synonym of 'impasse')

'unexciting partner' is the wordplay.
'unexciting' becomes 'stale' (I am not sure about this - if you are sure you should believe this answer much more).
'partner' becomes 'mate' ('mate' can be a synonym of 'partner').
'stale'+'mate'='STALEMATE'

'in' is the link.

Can you help me to learn more?

(Other definitions for stalemate that I've seen before include "Possible outcome of chess game" , "situation without a winner" , "Unresolvable position" , "Possible chess game ending" , "Inglorious deadlock" .)

I've seen this clue in The Telegraph.

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