Vietnam were offensive from the start of the game, hoping to break their series of losses with fan support on home ground.
But it was another defeat for them in the final round of the World Cup qualifiers, and the second against Saudi Arabia. They had lost 1-3 in the first leg.
Saleh Al-Shehri scored in the 31st minute, heading it from a cross from the right flank.
Saudi Arabia netted again with a tap-in from the second half. But after reviewing the situation on VAR, the referee called off the goal as Vietnamese defender Nguyen Thanh Chung was fouled.
Vietnam had several strong attacks towards the end of the game, but none of them succeeded.
With another victory, Saudi Arabia secured their top position of Group B.
Vietnam remain at the bottom of the group with zero points. They will play Australia again in January and China in February.