So then we must believe God in all things, for in all things God is true. Now that there was a Son of God, and that He existed not only before He appeared in the world, but also before the world was made, Moses, who was the first that prophesied says in Hebrew: Baresith bara Elowin basan benuam samenthares. And this, translated into our language, is: “The Son in the beginning: God established then the heaven and the earth.” This Jeremiah the prophet also testified, saying thus: Before the morning-star I begat thee: and before the sun (is) thy name; and that is, before the creation of the world; for together with the world the stars were made. And again the same says: Blessed is he who was, before he became man. Because, for God, the Son was (as) the beginning before the creation of the world (Irenaeus, Demonstration, 43)
He makes an even clearer ontological distinction a bit later:
So then the Father is Lord and the Son is Lord, and the Father is God and the Son is God; for that which is begotten of God is God. And so in the substance and power of His being there is shown forth one God; but there is also according to the economy of our redemption both Son and Father. Because to created things the Father of all is invisible and unapproachable, therefore those who are to draw near to God must have their access to the Father through the Son. (Irenaeus, Demonstration, 47)
So the Son is as the beginning of creation, in other words, he is not eternal. The Son’s begetting is not presented as being eternal, but “before” creation, which seems to put it in a sequence.