Precisely perform first two parts of lyric by former partner (7)
I believe the answer is:
exactly
'precisely' is the definition.
(synonyms)
'perform first two parts of lyric by former partner' is the wordplay.
I cannot really understand how this works, but
'perform' could be 'act' (acting is a kind of performing) and 'act' is present in the answer.
'by' could be 'x' (multiplication sign) and 'x' is found within the answer.
'partner' could be 'e' and 'e' is located in the answer.
This explanation may well be incorrect...
(Other definitions for exactly that I've seen before include "Dead" , "on the spot" , "how one might express agreement?" , "Quite so" , "in nice way" .)