Omid Garachomaghloo opened the scoring for Iran, the 2018 champion, just two minutes into the match.
Erfan Khodadadian doubled the lead 14 minutes later.
Hong Kong fought to pull a goal back through Yiu Tsz Leong in the 23rd minute but was unable to stop Iliya Ahmadimanesh from restoring Iran’s two-goal lead nine minutes later.
Garachomaghloo shined with goals in the 50th, 88th and second minute of added time while Khodadadian netted in the 84th minute to seal the emphatic win.
Iran will meet North Korea on Wednesday.