You only get to use your get-out-of-jail-free card once, and the Wallabies accept they won’t be afforded a similar luxury in the Rugby World Cup semi-finals after cashing theirs in to escape with an extraordinary win over Scotland.

The Wallabies prevailed in a one-point thriller at Twickenham thanks to a controversial 80th minute penalty goal to sharpshooter Bernard Foley following a see-sawing match in which they appeared destined for an early-than-expected exit.

The last-gasp 35-34 victory on Sunday (Monday AEDT) set up a semi-final clash with Argentina back at Twickenham in a week’s time.

But the Wallabies will need to go up several gears – and will be desperate to have breakdown king David Pocock (calf) and line-breaking fullback Israel Folau (ankle) return from injury – if they are to keep pace with ever-improving Argentina, who charged into the semis with a 43-20 demolition of Ireland.

They have plenty of concerns, notably the scrum, which had been so good all tournament, was dominated and penalised.

And the injury toll mounted with starting loosehead prop Scott Sio to be assessed for elbow damage after leaving with his arm in a sling after a scrum collapse.

“The level goes up every week,” said captain Stephen Moore, who along with centre Matt Giteau was playing his 100th Test.

“It went up today from last week and it will up again next week. That’s the way it goes now.

“There’s only four teams left. Everyone’s performances will need to lift.”

The overwhelming favourites heading into Sunday’s match, shellshocked Australia trailed at halftime and were behind in the dying seconds before snatching victory on the back of a controversial penalty to secure the five-tries-to-three win.

“We made it really tough on ourselves and I think we used our get-out-of-jail-card tonight,” admitted Foley.

The match looked to have slipped away when Scotland centre Mark Bennett intercepted a crazy wide pass in defence from reserve prop James Slipper to score what looked like the match-winning try six minutes from time.

But they were given one last chance after an 80th minute offside penalty went in their favour – the Scots were adamant the ball came off Wallaby reserve Nick Phipps.

That came after a similarly tough call earlier in the half which resulted in Scotland winger Sean Maitland getting yellow-carded for an intentional knock-on, allowing the Wallabies’ to score a clever try down his vacant wing from a maul.

Foley had endured a forgettable afternoon, missing all three first-half kicks, but given the chance to win the match he stepped up confidently to boot Australia into a semi-final showdown.

“Sometimes in these games you only get an opportunity to win it in the last few minutes and that was the case tonight,” Moore said.

“Bernard stepped up under pressure and nailed that penalty and we got the win, so we move on now to next week.”

A despondent Scotland captain Greig Laidlaw lamented the last-minute penalty, and questioned why the video referee hadn’t been used to adjudicate – though rules dictate it can’t be called on in such a scenario.

Regardless, Wallabies coach Michael Cheika was unequivocal in his appraisal of the decision.

However, despite escaping with a win, Cheika will have much to think about following a display littered with handling errors.

“Usually if you kick a goal with a minute to go to win, it’s usually a pretty good escape,” Cheika said.

“But at the end of the day, five tries we scored in a quarter-final of a World Cup, you expect to be somewhere near the winning end of the game.

“Although we’ve got massive improvements in certain areas, our try-scoring ability was there.”

Even their famed defence, which had conceded just two tries through the pool games, cracked feebly as Scotland’s Peter Horne snuck over untouched, having picked up the ball at the back of the ruck.

Scotland’s other two tries were more fortuitous, as Tommy Seymour crossed after backing up in support when teammate Finn Russell charged down a Foley clearing kick, before Bennett’s extraordinary intercept try.

Argentina, with the likes of electric winger Juan Imhoff, are expected to throw even more at the Wallabies.

“They’re just a team with backs that are really quick and you’ve got to be very careful of them,” said Wallabies great Michael Lynagh.

The Wallabies’ scrum, lauded after wins over England and Wales, also felt the pressure of the situation with loosehead prop Sio frequently penalised, which Laidlaw happily converted into points en route to a 19-point haul of his own.

Drew Mitchell scored two tries take his World Cup tally to 14, just one behind all-time leaders Jonah Lomu of New Zealand and Bryan Habana of South Africa.