Expert, one in a suit (3)
I believe the answer is:
ace
This clue is a double definition.
'expert' is the first definition.
(ace can informally mean very good)
'one in a suit' is the second definition.
(as in a card suit)
(Other definitions for ace that I've seen before include "The opponent can't return this serve" , "Virtuoso" , "'wicked'!" , "Tennis winner" , "Brilliant" .)