The victory also sends Team Melli top of Group D.
At a wonderfully atmospheric Al Nahyan Stadium, two goals from Sardar Azmoun ensured the Iranians made it six points from six – an impressive start to a campaign which will see the three-time champion assured of qualification should Yemen draw or lose when they play Iraq in the group’s later game.
With Iran on top and Vietnam unable to launch a cohesive attack of its own, the almost inevitable breakthrough came on 38 minutes, Sardar Azmoun rising highest to head home a pinpoint Saman Ghoddos cross and send his side into the half-time break holding a crucial, if slender, lead.
Iran, clearly intent on scoring a second, continued to press, and its patience was duly rewarded on 68 minutes, Azmoun neatly gathering a Mahdi Torabi pass and firing past Van Lâm to extend his side’s advantage and register his third goal of the tournament.
Nguyen Quang Hai curled a late effort narrowly off target, but it mattered little to Iran as it held on to register a record ninth successive AFC Asian Cup group stage victory to further underline their title credentials.
Iran is set to complete its group stage fixtures against Iraq next Wednesday in Dubai, with Vietnam scheduled to face Yemen in Al Ain on the same day.