After their upset 1-0 win over Japan, the Socceroos only needed to avoid defeat by less than five goals in Jeddah to seal automatic World Cup finals qualification for the first time in 12 years.
Saudi forward Abdulrahman Al-Aboud scored in the 19th minute at the King Abdullah Sports City Stadium to make things tense.
But striker Mitch Duke teed up Connor Metcalfe to equalise in the 42nd minute, before putting Australia in front in the 48th.
In his 100th appearance, goalkeeper and captain Mat Ryan denied Salem Al-Dawsari from the penalty spot in the 84th minute to seal victory.
Exactly a year before the start of next year's finals in the United States, Canada and Mexico, Australia (19 points, +9 goal difference) qualify in the second automatic spot behind Japan (23 points, +27) and ahead of Saudi Arabia (13 points, -1).
The result underlines the stellar job Tony Popovic, unbeaten as national team manager, has done since taking over from Graham Arnold, who claimed just a point from Australia's first two games.
Herve Renard's charges join fourth-placed Indonesia in the next round of qualifiers.Â
Defender Alessandro Circati was replaced by Jason Geria, while Duke and Patrick Yazbek started ahead of Brandon Borrello and Ryan Teague.
Martin Boyle dragged a shot wide in the 18th minute and Saudi Arabia immediately took the ball up the other end and scored.
Attacking maestro Al-Dawsari, so often a thorn in Australia's side, lifted the ball to Firas Al-Buraikan then burst forward to get it back.
Al-Dawsari then squared the ball for Al-Aboud to tap home on the goal line.
Musab Al-Juwayr blasted over the bar in the 33rd minute before Australia responded.
Duke took possession on the wing then threaded a squaring ball for Metcalfe, who nailed his first Socceroos goal with aplomb.
Al-Dawsari blasted a long-range shot just wide of the post in first-half injury time.
Australia took the lead when Boyle whipped in a free kick and Duke rose to glance home his first Socceroos goal since January 2024.
Ali Majrashi received a straight red card for denial of an obvious goal scoring opportunity on Boyle in the 52nd minute but it was overturned following a lengthy VAR review.
Saudi Arabia received a late penalty when Jason Geria was ruled to have brought down Al-Dawsari but Ryan palmed the spot-kick away.
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