Team Melli was defeated against the African team 79-67 at the Guangzhou Gymnasium.
Tunisian star Salah Mejri won the match from Iran’s Hamed Haddadi.
Mejri scored 22 points for Tunisia and Aaron Geramipoor scored 18 points for Iran.
Iran will meet powerhouse Spain on Wednesday.
The first round of the group phase takes place from Aug. 31 to Sept. 5 and the second round of the group phase will take place from Sept. 6 to Sept. 9.
The top two teams from each group will advance to the second round of the group phase.
The 2019 FIBA Basketball World Cup is the 18th tournament of the FIBA Basketball World Cup for men's national basketball teams.
The tournament will also act as qualification for the 2020 Summer Olympics, which will take the top two teams from each of the Americas and Europe, and the top team from each of Africa, Asia and Oceania, alongside the tournament's host China.