That's a good one! (3)
This clue is a double definition.
'that's a good' is the first definition.
(thesaurus)
'one' is the second definition.
(ace has a value of one in some card games)
(Other definitions for ace that I've seen before include "Virtuoso" , "rare driving result?" , "Crack" , "In golf, a hole in one" , "Service that's never returned" .)
(Other definitions for haha that I've seen before include "The sound of laughter" , "Laugh" , "Ditch" .)