Pair winning almost immediately? (6)
I believe the answer is:
pronto
'immediately' is the definition.
(pronto can mean at once or quickly)
'pair winning almost' is the wordplay.
'pair' becomes 'pr' (abbreviation).
'winning' becomes 'on top' (whoever's on top is winning).
'almost' means to remove the last letter (most of the word but not all of it).
'ontop' with its last letter removed is 'onto'.
'pr'+'onto'='PRONTO'
(Other definitions for pronto that I've seen before include "Quick as you can, amigo" , "Italian telephonic greeting" , "Quickly, immediately" , "Quickly, promptly" , "Right now, immediately" .)