In general, ace observed opening (2,1,5)
I believe the answer is:
as a whole
'in general' is the definition.
(synonyms)
'ace observed opening' is the wordplay.
'ace' becomes 'a' (abbreviation).
'observed' becomes 'saw' (seen).
'opening' becomes 'hole' (hole is a kind of opening).
'a'+'saw'+'hole'='AS A WHOLE'
(Other definitions for as a whole that I've seen before include "completely" , "In general" .)