On the ‘versus’ page it shows you a progress bar to unlock ranked play, which says something to the effect of ‘counts once per race per day’, not ‘once per day’. After winning I noted it go up, but when I’ve then won with a different race, and seen the ‘first win of the day’ bonus XP added in results page, it then doesn’t increment that number again. This is true for vs AI and vs Unranked; it only counts /one win per day/, race regardless.
I assume this is a bug with the counter/unlock feature, since the internet wisdom suggests that it is/was indeed counted once per race. This caused a lot of frustration while trying to identify, as it did seem to intermittently go up ‘sometimes’, so it then it took a while before I started scrutinising it properly - and then of course the definition of ‘day’ added to the confusion!