Great display that sees champ finally clean up (4)
I believe the answer is:
pomp
'great display' is the definition.
'champ finally clean up' is the wordplay.
'finally' says to take the final letters.
'clean' becomes 'mop' (mopping is a kind of cleaning).
'up' says the letters should be written backwards (in down clue: letters go upwards).
The final letter of 'champ' is 'p'.
'p'+'mop'='pmop'
'pmop' reversed gives 'POMP'.
'that sees' acts as a link.
(Other definitions for pomp that I've seen before include "Great show" , "Ceremonial elegance and splendour" , "Excessive ceremony" , "Ceremoniousness" , "Stately and splendid display" .)