Quoc Hoang gifted Vietnam an early lead after 10 minutes, only to see his effort cancelled out by Cambodian captain Ky Rina four minutes later.
Vietnam were reduced to ten men in the 20th minute after captain Tien Long was shown a red card following his infringement on Bunthoeun Bunnarong in the box.
The Cambodian side was awarded a penalty but Ean Pisey failed to beat Vietnamese keeper Duy Dung from the spot.
Playing without their captain, Vietnam still managed to take control of the game and created a number of scoring opportunities.
Three minutes before the hour mark, Vo Nguyen Hoang pushed Vietnam into the lead again, dribbling pass two defenders and scoring from the inside box.
Substitute Ha Trung Hau made it 3-1 for Vietnam 11 minutes later, before Nguyen The Hung and Doan Chi Bao added two more goals in the last 10 minutes.
Cambodia managed to reduce the gap to 2-5 thanks to forward Ly Mael’s goal in the 74th minute.
The fabulous win placed Vietnam second in Group I, behind Australia, who demolished hosts Mongolia 10-1 in the later match.
Next up for Vietnam will be two clashes against Mongolia and Australia on September 22 and 24, respectively.
The qualification features 45 teams in ten groups, with the ten group winners and the five best runners-up qualifying for the finals, scheduled to be held in Malaysia.
