Passaro rallied from 1-3 in the fourth set and overcame heavy cramping to win the set in a tie-break.
In a battle of 21-year-olds in Milan, the American saved five set points to avoid falling behind by two sets before winning 2-4, 4-3(7), 4-3(4), 3-4(4), 4-2.
Matteo Arnaldi and Francesco Passaro will take on one another in the round-robin stage of the 2022 ATP Next Gen Finals on November 9.
In the ATP Next Gen groupstage match, Brandon Nakashima defeated Matteo Arnaldi with a score of 2-4, 4-3(7), 4-3(4), 3-4(4), 4-2.
The Colombian, who went as far as the third round of Wimbledon, defeated Max Purcell in his second qualifying match.