The Italian, 62nd in the world, qualified by winning earlier in the day ahead of the Argentinian Francisco Cerundolo (30th), 6-3, 7-6 (7/3).
This is the first career final for the 20-year-old who dominated his opponent of the day in 1:54.
For Alcaraz, this will be the 6th final, the fifth in 2022 after notably Madrid and Miami in the Masters 1000. So far, he has not lost any and intends to add a sixth singles title to his list, at 19 years old.
"He (Musetti) played great matches before the final. (I did) too so I'm very confident for the final and I hope to get the six out of six," said the Spaniard, who will become Monday the youngest player to break into the Top 5 of the ATP rankings since Rafael Nadal.
Juan Carlos Ferrero's protege had to battle in the first set against the 48th in the world, before winning in the tie break and then unfolding in the second set.
In the end, it took him 1h33 to dismiss Molcan.
His opponent on Sunday beat Cerundolo in 1h54 and this success will already ensure him to climb into the Top 50 ATP on Monday.
"It's a surprise for me because I wasn't playing my best tennis last week (in Bastad), so I didn't expect to be in the final here," Lorenzo Musetti revealed.
After a disputed tie-break, the Italian finally took advantage of his second match point to crack Cerundolo.
Italian Lorenzo Musetti, during his first round match against Greek Stefanos Tsitsipas, at the Roland-Garros tournament, May 24, 2022 Christophe ARCHAMBAULT AFP / Archives
He had previously attempted an underhand serve on his first match point, and while leading 5-4.
A daring but missed gesture which, fortunately for him, was without consequence.
© 2022 AFP