Winger Mark Nawaqanitawase and replacement hooker Lachlan Lonergan were the heroes as Australia fought back from 21 points down with 27 minutes remaining to snatch victory from the jaws of defeat at the Principality Stadium.
Nawaqanitawase bagged a second-half double and also played a key role in the lead-up to Lonergan's match-winning try, two minutes from fulltime, as the Wallabies recovered from 34-13 down.
Adding to the drama, the Wallabies lost skipper James Slipper to a head knock in the first half, with replacement prop Sam Talakai becoming the 51st player used by embattled coach Dave Rennie in a rollercoaster 2022.
The improbable victory relieved pressure on Rennie, who had been staring down the barrel of presiding over Australia's worst win-loss record in a calendar year since 1958 following a hat-trick of narrow tour defeats to France, Italy and Ireland.
Instead, it was Wales coach Wayne Pivac who ended the match trying to save his job.
"Pretty stoked," Lonergan said.
"We were in the trenches there in the first half. At the start of the game, all we wanted to do was get a result and do whatever we had to do to do that.
"At halftime we came together and said 'we need to get a result'. Obviously our captain went down with that head knock. So as a team, we said we had to do it for him, our country, do it for Australia."
With nine players, including big guns Michael Hooper and Taniela Tupou, ruled out of the tour injured, Rennie only had 25 players to choose from for his match-day 23 on Saturday.
And with Slipper gone and his side falling more than 20 points behind after two converted tries to Wales early in the second half, the Wallabies looked dead and buried.
But Nawaqanitawase sparked the comeback with tries in the 57th and 67th minutes before another inspired burst set up Lonergan's game-breaker at the death.
Nawaqanitawase's heroics came after he started the Super Rugby season on the bench for the Waratahs.He then fielded a phone call from Rennie while on holidays in New Zealand last month to return home to Sydney to make his Wallabies debut in the season-ending tour.
"I guess that's life," said the humble 22-year-old.
"Things go up and down sometimes, but I'm grateful for where I am at the moment and I couldn't score those tries without the boys."
Australia's great Houdini act was also a psychological boost ahead of next year's Rugby World Cup in France, where they will face Wales in the pool stages.
"As you can see by the other games, we've only lost by a point to the top teams so don't lose faith in us," Nawaqanitawase said.
"We've got a strong team here. We back ourselves so hopefully everyone else backs us as well."
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