The Iranian team defeated Puerto Rico in straight sets (25-19, 25-14, 25-18) in Varna, Bulgaria.
Mohammad Mousavi led Iran with 11 points and Maurice Torres was Puerto Rico’s top scorer.
Iran is in Pool D along with Bulgaria, Puerto Rico, Poland, Finland and Cuba.
The 2018 championship is the 19th staging of the FIVB Volleyball Men's World Championship, contested by the senior men's national teams of the members of the Fédération Internationale de Volleyball (FIVB), the sport's global governing body.
The final tournament is being held in Italy and Bulgaria from September 9 to 30. For the first time the tournament is jointly-hosted by more than one country.
The final six will be hosted by Italy at the Pala Alpitour in Turin.