Dull detail about champion's final exchange? (5,5)
I believe the answer is:
match point
'final exchange?' is the definition.
(tennis)
'dull detail about champion's' is the wordplay.
'dull' becomes 'mat' (mat as opposed to glossy).
'detail' becomes 'point' (synonyms).
'about' is a charade indicator (letters next to each other).
'champion' becomes 'ch' (I've seen this in other clues).
'point' after 'ch' is 'chpoint'.
'mat'+'chpoint'='MATCH POINT'
(Other definitions for match point that I've seen before include "could lead to victory in court" , "Decisive moment in game" , "One scored at bridge, perhaps" , "One serve away from victory" , "a single ace away from victory" .)