613 mitzvos is from Torah Tzivah Lanu Moshe

Avodah
1

In the Chinukh, the Aseres haDiberos include mitzvos no.s 25 - 28,
14 mitzvos. So much for "10 Commandments". Kedarko, with only a couple
of exceptions, he follows the Rambam. So, #25 is "Anokhi".

R' Chesdai Crescas gave two cogent arguments against counting Anokhi:

1- He didn't understand how we can be commanded in something over whch we
have as little volition as what seems true to us.
2- How can you be commanded to believe in the One commanding? The very
existence of the mitzvah presupposes that one already got past it.

But even without Anokhi, there is no problem without getting to 10,
because there isn't a 1-to-1 from diberos to mitzvos anyway.

The bigger problem is that this whole thing of counting mitzvos is based
on R' Simlai, so the first two diberos, the ones heard directly miPi
haGevurah, have to be two mitzvos (plus the 611 tzivah lanu Moshe).
Judging from the parashah breaks, that means 20:2-6 and 20:7 includes
only two mitvos. (Interestingly, the break after the second diberah is
pesuchah. It is the only pesuach within the diberos. Fits the chazal
we're discussing.)

But... The first dibera includes Chinukh no.s 25-28 (Anokhi, Lo YihYeh,
Lo Sa'aseh, Lo Sishtachaveh), and the 2nd -- #29, lo lishava shav.
The Semag has a similar list for these pesuqim, except in his numbering,
it's Asei #1, followed by Lavin no.s 1, 20, 18, and 238.

So, if the Jews couldn't handle the first two diberos, that comes to 5
mitzvos heard miPi haGevurah + the 611 we received via Moshe!

(You would have to not count Anokhi AND count the three about AZ as one
mitzvah to get 2 + 611.)

How do rishonim who are trying to give peshat in R' Simlaei's 613
doing so in a way that contradicts his ra'ayah for the idea?

Tir'u baTov!
-Micha

2

Not that this answers your question, but surely #29 is the *third* dibber.

3

The Ramban on the Sefer HaMitzvos asks the same question on the Rambam -
how can the Rambam count 4 lavin of avodah zarah in the second dibra if R'
Simlai only leaves room for 1?

The Meshech Chochma (20:3) suggests that the Rambam is l'shitaso in Moreh
Nevuchim that Klal Yisroel did not hear any individual words from Hashem;
rather, all they heard was a Kol Elokim. In this light, R Simlai does not
mean that they heard the words "Anochi..." and "Lo Yihyeh…" from Hashem in
the same manner that they heard the other mitzvos word-for-word from
Moshe. Rather, they heard a Kol Elokim. And once they heard this Kol
Elokim, they knew, beyond any shadow of the doubt, that 1) there exists a
Borei and that 2) there was nothing else in the world that can compare to
this Borei.

Josh