The 0-4 loss in Melbourne saw Vietnam forfeit 9.46 points and go out of the top 100 for the first time since they entered it in November 2018.
They can make a return if they beat China in their next World Cup qualifier in Hanoi on February 1.
A victory will fetch 15.47 points and possibly put them in 98th place.
A draw will earn them 2.97 points while a loss will take away 9.53 points and lead to a further ranking slide.
China dropped one place to 75th after a 0-2 loss to Japan in another qualifier Thursday.
Both Vietnam and China are out of the race to qualify.