Mohammad Aamer (AP)

Aamer took three wickets for just 12 runs in 16 balls to leave Australia 215 for five in their second innings at lunch on the third day - a lead of 45 with just five wickets standing.

But Michael Clarke, the last of Australia's recognised batsmen, was 76 not out, having started the day unbeaten on 32 and wicketkeeper Tim Paine, who top scored with 17 in the first innings, was 17 not out.

The sixth-wicket pair had checked Pakistan's progress with a stand so far worth 51.

Aamer's current second innings return of four for 53, in what was his 10th Test, meant he'd already surpassed his previous Test-best match figures of six for 112 against Sri Lanka in Galle last year.

The 18-year-old left-armer had been unplayable at times while taking three for 20 as Australia were routed for just 88 in the first innings - their lowest Test total since being dismissed for 76 by the West Indies at Perth in 1984.

And his latest display meant Pakistan could think of ending a run of 13 straight Test defeats by Australia - a record sequence for one country against another.

Australia resumed on their overnight score of 136 for two, 34 behind Pakistan's first innings 258.

Ricky Ponting, the Australia captain, was 61 not out, having become in the course of his innings only the second batsman, after India's Sachin Tendulkar, to score 12,000 Test runs.

But Ponting had added only five more when he drove loosely outside off stump against Aamer and was caught by wicketkeeper Kamran Akmal for 66, having put on 89 for the third wicket with Clarke.

New batsman Michael Hussey, out for five in the first innings, had made eight when he failed to jab down on a lifting Aamer delivery and was well caught low down at second slip by Umar Akmal.

Australia were looking to prey on Pakistan's memories of the Sydney Test in January where they won by 36 runs despite a first innings deficit of 206.

But Aamer gave Australia plenty more to think about when he had Marcus North playing on for nought.

Meanwhile the luckless Asif got no reward for maintaining an excellent line and length.

Clarke though held firm to complete a 99-ball fifty and the vice-captain then nudged Australia's side into the lead.

That Pakistan's first innings advantage was 'held' to 170 was largely down to medium-pacer Shane Watson's return of six for 33 in 11 overs.

It was the second time in as many matches Watson had taken Test-best figures after his return of five for 40 in Australia's 150-run series-opening win at Lord's last week.

This series is being played in England because of security concerns in Pakistan, where international cricket was effectively suspended following an armed attack on Sri Lanka's team bus in Lahore in March last year.