Completion of a southern hemisphere sweep of the Rugby World Cup quarterfinals took some unexpected twists and turns before Australia edged Scotland in a dramatic finish at Twickenham on Sunday to line up a semifinal clash with Argentina.
The Pumas, seen as the least likely to reach the last four before the weekend, scored four tries in a convincing 43-20 victory over injury-depleted Ireland in Cardiff before the Scots threatened a big upset in London.
Scotland, who had beaten the Wallabies in two of their last three tests, led 16-15 at halftime and 34-32 going into the final minute in a downpour only to lose 35-34 after flyhalf Bernard Foley kicked a controversial penalty at the death.
Both semifinals will be played at Twickenham next weekend with holders New Zealand taking on South Africa in the other after a Six Nations team failed to reach the last four for the first time.
Scotland had a second semifinal since 1991 within their grasp but South African referee Craig Joubert would not be swayed in his decision to give Australia the last-gasp penalty in a controversial offside decision at a lineout.
Before that, Australia had scored five tries, two by Drew Mitchell, who took his World Cup tally to 14, one short of joint record holders Bryan Habana of South Africa and former All Black Jonah Lomu.
Scotland's reply in a match that swayed one way then the other included three tries and 19 points from the trusted boot of their inspirational captain Greig Laidlaw.
A gutted Laidlaw, the tournament's top scorer with 79 points, wondered why Joubert had not checked with the TMO on his penalty decision when the ball had appeared to come off a Wallaby jersey.
"They go to the TMO for everything else. It was such a big decision, why didn't they go to the TMO for that?" asked Laidlaw.
Despite Scottish frustration, a World Rugby spokesman said the South African had been right and that such an incident did not fall under the protocols for involving the TMO.
Australian coach Michael Cheika said: "It's a penalty and that's the way it works. You've still got to kick it."
That is what Foley, not at his place kicking best earlier in the match when he missed three conversions, did from the touchline.
Cheika also admitted to Australia having maybe played into Scottish hands by sticking to their favoured running rugby, saying: "We didn't go to a kicking game, maybe that was a bit naive from me. Maybe we shouldn't have opened it up for them."
Earlier, Argentina made a scintillating, almost error-free start to their quarterfinal at the Millennium Stadium and ran up a 17-0 lead with their first two tries by centre Matias Moroni and wing Juan Imhoff always appearing to have one and sometimes two men extra in their attacks down the wings.
Ireland, deprived through injury of top players including flyhalf Johnny Sexton and captain Paul O'Connell, fought back to within three points early in the second half at 23-20 down after tries by Luke Fitzgerald, thanks in part to a yellow card for prop Ramiro Herrera, and Jordi Murphy.
But the last 15 minutes belonged to Argentina, with tries from fullback Joaquin Tuculet and a second for Imhoff, a sign of the progress in the last four years of Rugby Championship experience by a side who in the past failed to stay in the game for the full 80.
Imhoff, whose tries took his Argentine World Cup record to seven, said the Pumas defence had made the difference.
"Ireland played with a great intensity. We are a really good team in offence. But today we had a defence to make the difference," he said.
That defensive effort included a fine contribution with 10 tackles by flyhalf Nicolas Sanchez, more noted for his distribution and kicking which yielded 23 points.
It was Argentina's third win in four World Cup meetings with the Irish, a rivalry that has marked the Pumas' progress since they reached their first quarter-final in 1999.