Australia outmuscled Wales 25-19 on Friday despite having only 13 players for most of the second half to earn a second win from their three WXV games.
Flanker Siokapesi Palu was sent off for a high tackle a minute after the break but Australia still outscored the Welsh by four tries to two in Auckland.
The Australians briefly lost another player for 10 minutes in the second half when lock Sera Naiqama was shown a yellow card.
"I couldn't be more proud of the girls. We stayed in there, we fought when down to 13 players and never gave up," said Australia No 8 Kaitlan Leaney, player of the match.
The Welsh ended their campaign with a third defeat, having been routed by hosts New Zealand last weekend after also losing to Canada.
England, the only team with two wins from two, can lift the WXV trophy on Saturday with a victory over New Zealand in a repeat of the World Cup final last year.
Australia opened the scoring when wing Maya Stewart, who missed last Saturday's win over France with a head injury, crossed for an early try.
Wales roared back as hooker Carys Phillips barrelled over from a driving maul for a converted try, before a penalty by Carys Dallinger saw Australia lead 8-7 at halftime.
With Palu already off, Australia had Naiqama yellow-carded when the Wallaroos' forwards conceded a penalty try with the Welsh pack hammering the try line.
Wales deserved their 14-8 lead, but Australia grabbed the momentum by steaming into the lead with three tries.
Prop Eva Karpani powered her way over the line, then replacement back Lori Cramer exploited poor defending to touch down, before wing Ivania Wong also crossed out wide.
Wales replacement hooker Kelsey Jones crashed over for a late try but Australia claimed back-to-back victories having stunned France 29-20 last weekend in Dunedin.
"We're extremely gutted with that one," Wales coach Ioan Cunningham said.
"We've thrown it away, especially when they were down to 13 players."