Pakistan made a disastrous start to the third Test in Sydney on Wednesday, losing four wickets in the opening session with Australia well on top in their hunt for a series clean sweep.

At lunch, the tourists were 75 for four with skipper Shan Masood on 32 and wicketkeeper Mohammad Rizwan 12. Pat Cummins had taken 2-16 from five overs.

It was a rousing morning session for the Australians, who are looking to send out 37-year-old opening batsman David Warner as a winner in his 112th and final Test match in his home city.

Pakistan won the toss but lost both openers Abdullah Shafique and debutant Saim Ayub inside the first two overs.

The out-of-form Shafique fell on the second ball of Mitchell Starc's opening over, needlessly playing a loose drive and nicking a catch to Steve Smith at second slip for a duck.

Ayub, brought in for Imam-ul-Haq to make his Test debut, only lasted two balls before he fell to a Josh Hazlewood outswinger in the next over, snapped up behind by Alex Carey.

Pakistan lurched to four for two and for a time looked to be consolidating with Babar Azam playing three glorious cover drives to the ropes before he was out on first-hour drinks for 26.

Cummins appealed vociferously for lbw but was turned down by the umpire, only to seek a review and get the verdict he sought, leaving the tourists tottering at 39 for three.

Saud Shakeel copped a nasty blow on the collarbone from a Cummins lifter and in the Australian skipper's next over he prodded a catch behind to Carey for five, leaving his side further in the mire at 47 for four.

Australia clinched the three-match series with a tense 79-run win in the second Test in Melbourne over Christmas.