Accurate performance by former partner (5)
I believe the answer is:
exact
'accurate' is the definition.
(I know that accurate can be written as exact)
'performance by former partner' is the wordplay.
'performance' becomes 'act' (act is a kind of performance).
'by' says to put letters next to each other.
'former partner' becomes 'ex' (an ex-partner).
'act' after 'ex' is 'EXACT'.
(Other definitions for exact that I've seen before include "Precisely correct" , "correct in every detail" , "Precise - demand" , "Precise and strictly correct" , "Not approximate; inflict (revenge) on someone" .)