Surprise victory (5)
I believe the answer is:
upset
'surprise victory' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for upset that I've seen before include "Distressed; overturn" , "Unexpected sports outcome" , "Perturbed - unexpected defeat" , "Distressed - surprise" , "Disturbed or knocked out of place" .)