TT Champion crashes a moment before victory (5,5)
I believe the answer is:
match point
'a moment before victory' is the definition.
(point which will allow a player to win a match)
'tt champion crashes' is the wordplay.
'crashes' indicates anagramming the letters.
'tt'+'champion'='ttchampion'
'ttchampion' with letters rearranged gives 'MATCH POINT'.
(Other definitions for match point that I've seen before include "One serve away from victory" , "a single ace away from victory" , "that may bring victory" , "could lead to victory in court" , "Decisive moment in game" .)