Goodness, one's a yes, at first (1,3)
I believe the answer is:
i say
'goodness one's a yes at first' is the definition.
I can't judge whether this defines the answer.
'one's a yes at first' is the wordplay.
'one's' becomes 'i's' (Roman numeral).
'at first' says to take the initial letters.
The initial letter of 'yes' is 'y'.
'is'+'a'+'y'='I SAY!'
Can you help me to learn more?
(Other definitions for i say that I've seen before include "Blimey!" , "Gosh!" , "Expression of surprise" , "Look here; oh, my" , "Exclamation of surprise" .)