Did Darwin have to explain where that first cell came from in order to put forth his theory? No.
I'm going to jump in and reiterate what I've seen posted many times on the forum evolution
does not equal "where that first cell came from". So, there is a pretty obvious difference between ToE and ID.
1) ID, has the requirement of positing a source for this ID i.e. the Creator because those who believe in ID are by default trying to attribute everything to a single entity.
2) In contrast, since ToE's goal is not trying to attribute abilties/features to a single entity the theory is under no obligation to say "where that first cell came from"!