In Oedipus Rex, Oedipus has fulfilled his terrible prophecy long ago, but without knowing it. He has already fallen into his fate. One could argue that he does have free will, however, in his decision to pursue the facts about his past, despite many suggestions that he let it go. In this argument, Oedipus's destruction comes not from his deeds themselves but from his persistent efforts to learn the truth, through which he reveals the true nature of those terrible deeds. Oedipus himself makes a different argument at the end of the play, when he says that his terrible deeds were fated, but that it was he alone who chose to blind himself. Here, Oedipus is arguing that while it is impossible to avoid one's fate, how you respond to your fate is a matter of free will.
Blind who now has eyes, beggar who now is rich,
he will grope his way toward a foreign soil,
a stick tapping before him step by step.