A 25-16 first Test loss in Sydney meant that Wales dropped to 11th place - they have been overtaken by Fiji - only five years after briefly being ranked world No 1.
It is the first time since World Rugby launched their rankings in 2003 that Wales have fallen outside the top 10.
They meet the Wallabies again on Saturday, when another loss would make it nine Tests on the bounce since beating 2023 World Cup pool-stage opponents Georgia.
Wales' worst run since they began playing international rugby 143 years ago was 10 games in 2002 and 2003 under New Zealander Steve Hansen.
That sequence included two Tests against New Zealand, while also incorporating a Six Nations wooden spoon.
This time around, Wales have lost to Argentina, Scotland, England, Ireland, France, Italy, South Africa and Australia, with head coach Warren Gatland's Test record for his second stint in charge showing 14 defeats from 20 starts.
And life is unlikely to become any easier, with the Melbourne clash being followed by autumn Tests against Fiji, Australia and South Africa before Wales open their 2025 Six Nations campaign by tackling France in Paris.
Speaking immediately after the Sydney setback and asked about lifting his players for Melbourne, Gatland said: "I don't think we have to raise them. The way the boys have trained and the buzz around them, they have been outstanding.
"We know we are going through a process playing at the highest level, which is about learning to handle some pressure.
"It is just staying in the arm-wrestle. That takes a little bit of time in terms of on-the-field stuff. I have been through that with other teams in the past.
"Once you get across the line, players in the team learn that understanding and turn those games that are close into wins. That is what we have got to work through at the moment.
"When you win once, you build confidence and learn how to close out games. There are a lot of inexperienced players who are going through that process.
"It is about taking the lessons (from the first Test) and applying them, saying 'where can I improve my game and be better next week'?"
Gatland will need to assess the fitness of prop Gareth Thomas after he was forced off injured in Sydney.
Thomas, who was yellow-carded during the first half, made way for Kemsley Mathias early in the second period following a blow to his leg.
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