The Infernal Machine (1947)

Cocksure and convinced of his own magnificence, the young Oedipus only vanquishes the Sphinx because she lets him. In the form of a young woman she falls in love with Oedipus as soon as she lays eyes on him, and actually tells him the answer to the riddle before she asks it - but not before she has easily reduced him to a state of abject, gibbering terror. Once he realizes he isn't going to die, he answers the riddle as if he's come up with the answer all by himself, then hightails it for Thebes to claim his reward.