Top card for pro (3)
I believe the answer is:
ace
I believe this is a double definition.
'top card' is the first definition.
(I've seen this before)
'pro' is the second definition.
(I've seen this in another clue)
'for' acts as a link.
(Other definitions for ace that I've seen before include "Hole in one; very good" , "Single unit on playing cards" , "Expert; one" , "Expert - winning serve" , "rare driving result?" .)