Nasir Jamshed’s 55 helped Pakistan to 149-6 before their spinners took over.
Saeed Ajmal returned 3-17 and Mohammad Hafeez and Hasan Raza took two wickets each in Australia’s 117-7.
Australia reach the last four on net run-rate, while Pakistan need South Africa, who have now been knocked out, to beat India later today or it comes down to run-rate to separate the two.
While Australia, who were beaten finalists in 2010, will be pleased to reach the final four alongside Sri Lanka and West Indies, they will need to work out a way of playing spin successfully on turning wickets.
Through some sensational performances by Shane Watson, who has scored the most runs, taken the most wickets and hit the most sixes in the competition, they had bludgeoned their way to a 100% record heading into the game.
However, once their opener was leg-before to Hasan for just eight when failing to connect with a sweep, the Australia batting order suddenly looked top heavy.
It was trial by spin, with Pakistan waiting until the 18th over before using paceman Umar Gul, and David Warner fell in similar style to his opening partner as he failed to get bat on ball to Hafeez.
Only Michael Hussey looked comfortable in the middle as he expertly kept the scoreboard ticking over with his canny ability to work the ball into space for ones and twos.
Skipper George Bailey was Hussey’s only realistic partner to overhaul the target, and when he was also trapped in front, this time by Saeed Ajmal, the Australia innings turned from a run-chase into a salvage mission.
The Aussies knew they only needed to score 112 to ensure their place in the final four on net run-rate, and Hussey made sure he saw them to the target.
Ajmal was bowling with the same masterful menace and mystery which saw England slump to a 3-0 Test series defeat to Pakistan last winter, and when he dismissed Matthew Wade and Pat Cummins in the penultimate over the game was effectively over.
Pakistan’s spinners were grateful to Jamshed’s classy half-century after being put in to bat, the 22-year-old batting with style and intelligence to help his side recover from 29-2.
He shared a 79-run partnership for the third wicket with Kamran Akmal (32) before Mitchell Starc, who impressed with figures of 3-20, dismissed the wicketkeeper.
Some late hitting from Abdur Razzaq boosted Pakistan’s total before the bowlers took charge.
