The win sees Australia through to their sixth straight World Cup and through to the Asian Cup Semi-Finals for a fourth straight tournament, keeping their title defense alive.
Vietnam needed a win to advance, and had a big following as the host nation, keen to cheer them through to their first World Cup.
Vietnam were building their performance on a solid defense and look to break down Australia on the counter.
Australia very nearly had a goal inside the first five minutes as Lisa De Vanna was able to find an unmarked Michelle Heyman at the far post, only for Heyman to head over the bar.
Vietnam responded well as Tuyet Dyung was able to run and get a chance away but sent her effort well over the bar, before their next chance came, only for Australia to desperately clear the ball to safety.
Australia were by far the dominant force with Emily van Efmond, Alanna Kennedy and Calre Polkinghorne all had great opportunities but could not find the target.
Australia could well have hit the lead in the 38th minute as Caitlin Foord made a great run in and linked with Heyman but could only send her effort, on the return pass, in to the side netting.
The goal came from a rare moment as Australia were awarded an indirect free kick in the box after a back pass was ruled to have happened despite some speculation that the back pass was not intentional.
Van Egmond sent in the direct free-kick, looking to take a touch off the Vietnam wall, thus meeting the indirect requirement, and the play worked as the ball deflected in to the net off of Le Thi Thuong to give Australia a 1-0 half-time lead.
Australia continued to be the stronger side after thebreak with van Egmond able to force a good save out of Tuyet May after a powerful shot from the edge of the area.
Being in Vietnam the weather changed and started to affect the match as the rain came fown, making life tough for both sides.
Australia thought they had their second goal just after the hour mark as Lisa De Vanna was able to hit a shot that saw a deflection and went agonizingly wide.
In the 82nd minute Vietnam nearly found a goal as Nguyen Thi Nguyet was able to use her speed and unleash a shot that Australia scrambled back to clear.
In the 90th minute Katrina Gorry sealed the match as she received the ball on the edge of the area and unleashed a rocket of a shot that left the keeper with no chance.
Australia will play the winner of the Korea Republic v China match on Monday in the semi-final which will be played on Thursday.