Fresh off their upset 3-1 victory over Japan, who knocked them out of last year's FIFA World Cup, the Matildas displayed an air of confidence from the outset.
And they only had to wait 10 minutes to open the scoring with Emily Gielnik adjudged to have beaten the offside trap after a clever through ball from Simon.
Gielnik made no mistake from inside the six yard box and bagged her first goal for the Matildas at senior level in the process.
But Australia's Women's side smelt blood in the water and added goals in the 16th and 19th minutes to stretch their lead to 3-0.
First it with Simon, who produced a sublime first touch and turn, before slamming the ball into the back of the net.
Then Alanna Kennedy scored her first goal for the Matildas, with the 21 year-old's left-footed finish coming after an incisive run in the lead-up.
But Simon then stole the headlines, bagging her hat-trick after goals in the 38th and 43rd minutes, although the latter strike appeared to take a deflection after her shot came from an acute angle.
Ashley Sykes, Emily van Egmond, Michelle Heyman and Clare Polkinghorne each got on the scoresheet in the second stanza to complete the rout.
Matildas coach Alen Stajcic said he knew Vietnam would represent a different proposition to their first up win over Japan and was pleased with the result.
“Obviously a good result for us today and a good performance against a team that makes it really hard to play against,” Stajcic said.
“Vietnam were very well organised, they worked hard for each other which we saw against China the other day, so I’m very pleased that we were able to score nine goals today and put together some good patches of football, but the best part is there is still room for improvement.”
But Stajcic said the Matildas can't rest on their laurels in the qualifying campaign for Rio 2016.
“Six points isn’t enough to get us to Rio, there is still a lot of football to be played,” he said.
“We’re two good steps down the track but there is still a long way to go and we know we’ve got three tough games ahead.
“We’ve made good strides forward but there is a long way to go and we’re not taking anything for granted.”
With the emphatic result, the Matildas maintain their lead at the top of their six-team qualifying group, with a top two finish enough to see them qualify for August’s Olympic Games.
Australia Women 9 (Simon 16', 38', 43', Gielnik 10', Kennedy 19', Sykes 64', van Egmond 68', Heyman 77', Polkinghorne 85')
Vietnam Women 0
Yanmar Stadium Nagai, Osaka, Japan