At nightfall, Leporello, Don Giovanni's servant, stands guard in front of the Commendatore's palace, where his master has entered in order to seduce his daughter Donna Anna. He laments his condition: "Night and day I slave for one who does not appreciate it, ... I want to be a gentleman and to give up my servitude" (introduction: "Notte e giorno faticar")
 
Suddenly, Anna appears in a rage, pursuing Don Giovanni who is trying to hide his face; hearing his cries, his father, runs up and challenges the seducer to a duel, who mortally wounds him " Help ... the assassin has wounded me, I see my soul escaping…" (Trio: "Ah soccorso! »)[3].
 
Don Giovanni flees. Anna is in a state of shock, she recognized her father's body and fainted. Ottavio, her fiancé, came running and tries to comfort her as she regained consciousness. Both swear to avenge her “Ah! swear forever to avenge his blood if you can... I swear it upon our love... What an oath, ye gods” (Recitative and Duo “Che giuramento, oh Dei”).
 
The hunt is on! Already in search of a new adventure, Don Giovanni and Leporello meet Donna Elvira in the early morning, whom he once seduced and then abandoned. “Quiet! I think I sniff a woman” says Don Giovanni... “My, what a perfect sense of smell! » thinks Leporello aside.

Donna Elvira, is devastated by his betrayal “Ah, who will tell me where the rascal is whom, to my shame, I loved and who betrayed me?” (Aria "Ah, chi mi dice mai!"). But Don Giovanni does not recognize her immediately and tries to start a conversation. Having recognized her, he flees, leaving her with Leporello, who tries to console her by presenting the list of her master's conquests “My dear lady, this is a list of the beauties my master has loved” (Aria: “Madamina!”)[4]. Elvira makes a vow of revenge.
 
Later in the morning, Don Giovanni comes across a village wedding Zerlina is to marry Masetto (Duet with Chorus “Giovinette che fate all’amore”). Don Giovanni, all exhilarated, goes hunting again, Zerlina pleases him. The opportunity is too good, the seducer goes in force to stay alone with Zerlina. Masetto rebels, Don Giovanni threatens him "If you don't leave us right away, be careful, you'll regret it". Masetto bows bitterly “I understand, yes sir, I do!” (Aria: “Ho capito, signor si!”). Remained alone with Zerlina Giovanni goes on the attack trying to seduce Zerlina with sweet arguments. There follows a declaration of love in which Don Giovanni promises the moon to the young Zerlina "There we will be married, there you will give me your hand, there you will tell me yes, ... I will change your life..." (Duettino “La ci darem la mano”)[5]. Everything is feigned but with such expertise... that Zerlina, hesitant at first, is quickly conquered.

But the impromptu arrival of Elvira cuts short Don Giovanni's attempt. She trains Zerlina before she gives in and recommends that she flee the traitor (Aria “Ah, fuggi il traditor”). Then, she warns Donna Anna and Don Ottavio, who have come to seek the friendship of Don Giovanni, against the one who has abandoned her and whom they have not yet recognized, "Do not believe, unhappy one, in that faithless heart!, The villain has already betrayed me and now seeks to betray you too”. Don Giovanni responds to her reproaches by trying to pass her off as crazy “... the poor girl is mad, my friends”, without managing to convince her interlocutors who are beginning to have doubts (Quartet: “Non ti fidar, o misera. »). After his departure, Donna Anna thinks she has recognized in Don Giovanni's « farewell / addio » her father's murderer and tells Ottavio about the aggression (Recitative with orchestra and aria « Don Ottavio ... son morta! » )[6] .

We are now in the garden of Don Giovanni's palace. In a recitative, Leporello comes to report to his master what he has done with Mazetto and Elvira. “Well done excellently done!» Don Giovanni, delighted, instructs him to organize a party « So that the wine may set their heads whirling, go and prepare a wonderful party. If you find a young lady on the way, try to bring her along...I want to make love, to my list tomorrow morning, you will have to add at least ten names" (Aria "Fin ch'han dal vino")[7]. Pleasures and festivities will be on the menu of a masked ball to which Masetto, Zerlina, are invited. Mazetto is pissed at having been dismissed by Leporello. He does not know what exactly happened between his fiancée and the "cavaliero". Zerlina tries to appease his jealousy "You can beat me my beautiful Mazetto, I will stay here like a lamb... happy then I will kiss your wonderfully sweet hands... Let’s make up, my own true love …" (Recitative and aria "Batti, batti , o bel Mazetto”).

The grand finale of the first act comes. We are arriving to a turning point.

Don Giovanni did not give up trying to seduce Zerlina who tried to hide in a grove. He saw her "Zerlina my lovely I’ve seen you, don't run away ... I am full in love, I want to make you happy". These words are compromising, poor Zerlina is tortured. But the interview is cut short because Mazetto has just popped up “Mazetto? - Yes Mazetto! ". Don Giovanni manages to get out of an embarrassing situation. The two men will not face each other in the end. They are overtaken by the party "Le us cheer up, and go and dance with the others, all three of us …".