Former partner with performance that's accurate (5)
I believe the answer is:
exact
'that's accurate' is the definition.
(synonyms)
'former partner with performance' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'with' means one lot of letters go next to another.
'performance' becomes 'act' (act is a kind of performance).
'ex'+'act'='EXACT'
(Other definitions for exact that I've seen before include "Precise; extort" , "correct in every detail" , "Strict" , "Not approximate, precise" , "Correct; insist on" .)