As part morning, first extra sugar substitute (9)

I believe the answer is:

aspartame

'sugar substitute' is the definition.
(I've seen this before)

'as part morning first extra' is the wordplay.
'morning' becomes 'am' (as in 12:00 AM).
'first extra' becomes 'e' (1st letter of 'extra').
'as'+'part'+'am'+'e'='ASPARTAME'

(Other definitions for aspartame that I've seen before include "Sugar substitute" , "Strong artificial sweetener -- same apart (anag)" , "What sweetens" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.