Chance of success? Work up talent, I fancy (9)
I believe the answer is:
potential
'chance of success?' is the definition.
(as in a person with potential)
'work up talent i fancy' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'up' is a reversal indicator (in down clue: letters go upwards).
'fancy' indicates an anagram.
'op' back-to-front is 'po'.
'talent'+'i'='talenti'
'talenti' is an anagram of 'tential'.
'po'+'tential'='POTENTIAL'
(Other definitions for potential that I've seen before include "Inherent capacity not realised" , "Inherent, though latent, capacity" , "Latent; ability to develop" , "Likely, though not yet tested" , "Possible (capacities of a person or situation)" .)