Express quick Shaun Tait led Australia's attack with two wickets for 25 runs from his maximum four overs, although his return did include nine wides.
Umar Akmal and Shoaib Malik (21) revived the innings with a stand of 51 after Pakistan lost three wickets for two runs in six balls to slump to 47 for four in the eighth over.
An overwhelmingly Pakistan supporting crowd were silenced early on when Shahzaib Hasan fell to a first-ball duck, pulling Dirk Nannes to David Hussey at mid-on.
Tait, fresh from his 100mph delivery in the fifth one-day international against England at Lord's on Saturday, struggled for accuracy early on and his first two balls were wides.
Kamran Akmal, who also made a fine fifty in St Lucia, looked in superb touch as he pulled left-arm quick Dirk Nannes for six.But his exit sparked a top-order collapse.
Salman Butt played occasional off-spinner David Hussey behind point and appeared to decline a single quickly. But Kamran, already well down the pitch, was run out by Cameron White's throw to the bowler.
Next ball, Butt holed out in the deep and, soon afterwards, big-hitting Pakistan captain Shahid Afridi, who'd won the toss, was out for a golden duck when he missed a sweep off a Steven Smith full toss. Pakistan were now 47 for four in the eighth over.
But Umar Akmal struck leg-spinner Smith for two straight sixes as 15 runs came of the 10th over and 20 were taken off the 11th, from David Hussey, admidst a flurry of fours.
And when Nannes returned, Umar cleverly swept him to the fine leg boundary before Malik cut him for four to bring up a fifty stand in 47 balls.
But the duo added just one more run before Malik was out in controversial fashion after a Nannes delivery went through to wicketkeeper Tim Paine, whose reaction suggested he was uncertain whether the ball had carried.
Pakistani umpires Aleem Dar and Nadeem Ghouri eventually referred the decision to their compatriot Ahsan Raza, the third umpire.
Although replays appeared inconclusive, Raza gave Malik out for 21 and Pakistan were 98 for five off 12 overs.
But Umar continued to attack, hoisting left-arm quick Mitchell Johnson for a huge six and pulling him for four off successive balls to go to fifty off just 21 balls before he was bowled by Tait.
The second and final Twenty20 international takes place here on Tuesday, the matches being played in England because of concerns regarding the security situation in Pakistan.
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