Let us remind ourselves of what Aristotle said. He argues that a tragedy should be a tightly unified construction based on a single action and featuring a single protagonist, or hero. Aristotle argued that this hero should be a man or woman who is on the whole good, but whose downfall is brought about by some frailty or tragic flaw. Mostly, this flaw is based on arrogance. The tragedy consists of the hero going through reversals of fortune until he recognises the truth that has been hidden from him. In the process the hero experiences profound suffering.
Examining the plot of this excellent play reveals many similarities. It is indeed a tightly unified construction, and the tragic hero is obviously, in spite of the title, Creon. It is his stubborness that is his tragic flaw, as he seeks to secure his power by a show of strength forcing all rebels to be left unburied. It is Antigone's refusal to do this for her brother that leads to his stubborness in stating that she must be buried alive to starve to death and then leads to the death of his son and wife. It is only at the end of the play that he realises how stupid he has been and he is left a raving old man, having to cope with his isolation and what he has done. He realises his tragic flaw has resulted in this situation.