Oreste, overwrought, appears with Pilade, who tries to calm him. He declares his unrequited love for Ermione, but Pilade tells him that he must do his duty (Cavatina and duet: "Che sorda al mesto pianto" ... "Ah! come nascondere la fiamma vorace" / "She is deaf to my tears ... Ah, how can I hide this voracious flame"). A march announces the arrival of Pirro and Ermione, attended by Fenicio, Attalo, the grandees and guards. Andromaca also enters, but stays at the back of the stage. Oreste tells Pirro that he represents all the kings of Greece, who are agreed that Astianatte must die before he is able to avenge the death of Hector, his father. Pirro defies Oreste, saying that he will do as he wishes, and that Astianatte may even share the throne with him (Aria: "Balena in man del figlio l'asta di Achille" ... "Deh serena i mesti rai" ... "Non pavento: quest'alma ti sprezza" / "Achilles' spear flashes in his son's hand" ... "Brighten your gloomy gaze" ... "You cannot frighten me: my soul despises you"). Andromaca and Ermione are aghast, Oreste warns Pirro that the Greeks will be angry with him, and Pilade vows that he will save Oreste from Pirro's anger.