Completely; to the end (3,3,3)
I believe the answer is:
all the way
This clue is a double definition.
'completely' is the first definition.
(both can mean to the fullest extent)
'to the end' is the second definition.
(I've seen this before)
(Other definitions for all the way that I've seen before include "Without reservation" , "Completely" , "to the end" , "Sinatra sang this" , "without limit" .)