One at cards is excellent (3)
I believe the answer is:
I believe this is a double definition.
'one at cards' is the first definition.
(I've seen this before)
'excellent' is the second definition.
(ace can informally mean very good)
'is' acts as a link.
(Other definitions for ace that I've seen before include "Entertain" , "One in playing-cards" , "winner in court" , "'wicked'!" , "Girl" .)