Iran’s Abolfazl Mahdian and Matin Hosseini collected 12 points each and Gabriel Colon Ortiz Yann earned eight points for Puerto Rico.
Iran is scheduled to play Colombia and Nigeria in Pool C on Saturday and Sunday, respectively.
The 2023 FIVB Volleyball Boys' U-19 World Championship kicked off in San Juan, Argentina, on August 2 and will run until August 13.
The 20 participating teams were split into four single round-robin pools of five for the pool stage of the championship to be played over the first five competition days.