Point of no return for champion (3)
I believe the answer is:
ace
I believe this clue is a double definition.
'point of no return' is the first definition.
(tennis serve which is not returned)
'champion' is the second definition.
(both can mean a person excelling at something)
'for' is the link.
(Other definitions for ace that I've seen before include "Brilliant" , "Girl" , "Playing card - expert" , "The opponent can't return this serve" , "Playing card with a single symbol" .)