In the parallel text (4: 15.5) in Tasso's Gerusalemme Liberata, published in 1581 twelve years before, Satan said, "Fummo, io no 'l nego, in quel conflitto vinti," i.e. "In that conflict (I won't deny it) we have been defeated." The GC version puts it a bit more harshly.
But what is really worth noticing is the last two verses, that in GL were completely different: "Diede che che si fosse a lui vittoria: / rimase a noi d'invitto ardir la gloria," that is "Whatever gave Him victory, to us the glory of an unconquered boldness remains." This version may sound more daring than the GC one, and especially more Miltonian.
On the other hand, when in GC Satan calls himself the one who "moves the world" the sentence is not less daring at all. Indeed, it parallels God who "moves the sun and the other stars" (Dante, Paradiso, last verse), nearly suggesting a Gnostic-like worldview. In fact, this was one extreme of the swing of the pendulum in Renaissance theology, the other extreme being a Spinozian deification of Nature. Tasso clearly shows both in his long poem Il Mondo Creato (1592).