Triumphs by a good score, nominally (7)
I believe the answer is:
winston
'score nominally' is the definition.
The definition suggests a singular noun which matches the answer.
'triumphs by a good' is the wordplay.
'triumphs' becomes 'wins' (I've seen this before).
'by' is a charade indicator (letters next to each other).
'a good' becomes 'ton' (I can't justify this - if you can you should believe this answer much more).
'wins'+'ton'='WINSTON'
Can you help me to learn more?
(Other definitions for winston that I've seen before include "Prime minister" , "-- Churchill, UK PM" , "Statesman" , "Man" , "11 [LAWMAKER]" .)