Wales have kept out a spirited Australian side, claiming a 29-25 victory at Tokyo Stadium.
The Wallabies scored three tries to two and were the vastly superior team in the second half, but they paid for an error-riddled opening 40 minutes which lacked purpose and execution.
Wales were more clinical, adopting a more-conservative game plan in humid conditions that made the ball difficult to control.
Just as Nic White and Christian Lealiifano struggled to impose themselves in last week's opening win over Fiji, re-introduced pair Will Genia and Bernard Foley failed to stamp their authority.
Matt Toomua's injection off the bench soon after halftime provided a playmaking spark. He might have forced coach Michael Cheika's hand for next week's match against Uruguay.
Both captains were inspirational.
Welsh skipper Alun Wyn Jones, playing in his national record 130th Test, made a game-high 23 tackles.
Australia's Michael Hooper was arguably their player of the game for the second time at the tournament, having shone in the opening 39-21 win over Fiji, a game also marked by his team's second-half fightback.
Hooper and Dane Haylett-Petty scored second-half tries for the Wallabies, while veteran winger Adam Ashley-Cooper crossed in the first.
The loss is just the third Australia have suffered in the World Cup pool phase, after losses in 1995 to South Africa and 2011 against Ireland.