Australia were penalised a little more than 10 seconds into the match after captain Dave Porecki failed to roll away.
That set the tone for a match punctuated by penalty after penalty as Australia gave Wales every opportunity to skip away with the lead.
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Such was Australia’s lack of discipline that nearly half of Wales’ points came from penalties.
The thumping loss all but ends any hopes the Wallabies have of making the quarter-finals, notwithstanding shock losses for Fiji against Portugal and Georgia, and Australia winning their final match against Portugal.
Never, in the 10 editions of the Rugby World Cup, has Australia failed to make the quarter-finals. That fate is seemingly all but sealed.
Even before the match had concluded, the post-mortem had already begun.
“The simple matter is that their destiny is now well out of their hands,” said former Wallabies international Morgan Turinui on Stan Sport’s coverage.
“They would need Fiji to lose probably twice against Georgia and Portugal – and that is unlikely.
“Even then it might not be enough in terms of bonus points and the fact that Fiji beat Australia. At the end of this match, you can say that this will be it for the Wallabies.”
Wales break Wallabies defence inside three minutes for first try
Less than three minutes into the match, Welsh flanker Jac Morgan split the Wallabies defence wide open and roared towards the try line before offloading to Gareth Davies to open the scoring.
The Wallabies’ two sole scoring opportunities came in the ninth and 14th minute courtesy of penalty kicks. Beyond that, Australia hardly looked like threatening the try line.
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Wales lost first-choice fly-half Dan Biggar in the 12th minute but replacement Gareth Anscombe was more than up to the task.
Of his 10 shots at goal, Anscombe slotted eight. Six of them were penalties.
Wales break Wallabies spirits with extraordinary chip and chase try
Opportunities for the Wallabies to find gaps in the Welsh defence were few and far between.
Ben Donaldson gave Australia a glimmer of hope in the 17th minute when he burst through the line only to offload the ball to a Welsh player.
Rob Leota enjoyed a similarly strong run in the 25th minute only for Wales to turn it over.
Perhaps the best chance for Australia to score came in the 26th minute when a penalty earned them a line-out just five metres from the try line.
In a split second, the momentum swung as the Wallabies threw the ball long and into no man’s land before Wales kicked and earned a remarkable 50-22.
From that, the Wallabies conceded a penalty and gave Wales another kick at goal.
Australia were fortunate that the scoreline only read 16-6 at the break when the ball was held up in their own in-goal area after Wales went on a tear.
If the first half got off to a poor start, then the second couldn’t have started much worse. Wales turned the ball over almost immediately and within three minutes had their first shot at goal for another penalty.
Penalties continued to flow and with the ledger at 19-6 it was only in the 48th minute that Wales scored their second try.
A deft chip and chase into clear air set up by Anscombe allowed Nick Tompkins to score and draw the lead out to 26-6.
Wales sink knife into Wallabies with final try
The sixth and final penalty goal came in the 60th minute before a drop goal by Anscombe drew the score out to 35-6.
By the 75th minute, Wallabies fans were already on their way out of the stadium, consigned to defeat and the reality that their Rugby World Cup hopes were over.
Then, just two minutes shy of full-time, Wales twisted the knife with a driving maul off the back of a line-out to score their third try.
Morgan, who set up the first try, earned one of his own and sent Parc Olympique Lyonnais into raptures.
All told, the scoreline read 40-6. It marked the worst result for Australia at the Rugby World Cup and its biggest ever margin of defeat to Wales.