Kyle Hobus led the US with 19 points, while Amin Esmaeilnezhad collected 30 points for Iran.
Iran had lost to Brazil 3-0 in its first match.
Iran is scheduled to face Slovenia on Saturday.
The 2025 FIVB Men's Volleyball Nations League is the seventh edition of the FIVB Men's Volleyball Nations League, an annual men's international volleyball tournament.
The competition started on June 11 and will continue until August 3, 2025, with the final round scheduled to take place at the Beilun Gymnasium in Ningbo, China.