Perform only part of a play (3)
I believe the answer is:
act
This clue is a double definition.
'perform' is the first definition.
(acting is a kind of performing)
'only part of a play' is the second definition.
('act' is part of 'play')
(Other definitions for act that I've seen before include "Pretend to be - deed" , "Exploit" , "Function" , "Perform theatrically" , "Thing done" .)