Da'as Zekeinim (compilations of teachings from the Ba'alei Tosafos) to Genesis 1:1 ask a question on one of the first comments of Rashi:
ועוד פרש"י א"ר יצחק לא היה צריך להתחיל התורה וכו', וקשה שהרי כבר נצטוו, על מילה וגיד הנשה
Rashi explained further: "Rabbi Yitzchak says that the Torah should have started [with the first mitzvah, that of the Sanctification of the New Moon]". This is problematic, for [the Jews] were already commanded regarding circumcision and not eating from the sciatic nerve.
The Da'as Zekeinim are bothered with the implication that the first mitzvah in the Torah is the Sanctification of the New Moon, since there were already two other mitzvos previously commanded (see there for their answer).
What's very odd is they ignore the very first mitzvah that appears in the Torah, that of pru urvu/procreation (Genesis 1:28 according to the Chinuch, or Genesis 9:7 according to the Rambam). Why did they not mention this? Do they not hold it's a mitzvah1?
1 There's some discussion why Rav Saadiah Gaon left out the mitzvah of procreation in his listing of the 613 mitzvos:
ממה שלא מנה רבינו ז"ל במנין העשין עשה דפו"ר שמנאוה כל מוני המצות. והיא מצוה ברורה ומפורשת ואיך יתכן להשמיטה.
Apparently all those that spell out the 613 mitzvos count pru urvu in the list. One suggestion is his listing of kiddushin is really referring to pru urvu, similar to the opinion of the Rosh (Kesubos 1:12).
I'm not sure if this would help explain the Da'as Zekeinim, that they really hold it's not a mitzvah, like the simple reading of Rav Saadiah Gaon, and not like the above suggestion.