Karachi. Opener Abdullah Shafique and skipper Babar Azam kept Australia at bay as they guided Pakistan to 104-2 at tea on the fourth day of the second Test in Karachi on Tuesday.

Set a daunting 506-run target, Pakistan lost Imam-ul-Haq (one) and Azhar Ali (six) before Shafique and Azam led the fightback during their unbroken 83-run stand for the third wicket.

At the tea break Shafique was unbeaten on 44 and Azam 47. The hosts needed another 402 runs for an improbable win or to bat out the remaining four sessions for a fighting draw.

No team has ever chased more than the 418-7 that West Indies did against Australia at Antigua in 2003 while Pakistan's highest successful chase is a 377-run target against Sri Lanka at Pallekele in 2015.

Australia, resuming their second innings at 81-1, had batted for just 26 minutes at the start of play to add 16 runs before declaring on 97-2.

The visitors scored 556-9 declared in their first innings then dismissed Pakistan for 148.

The home team had hoped Azhar would anchor the second innings but the senior batsman fell in a comical way, bowled lbw by Cameron Green when trying to evade a short-pitched delivery.

Azhar chose not to review as he trudged off but was left to regret it as television replays showed he had gloved the ball.

Australia could have had Shafique on 20 but the experienced Steve Smith spilled a straightforward catch in the slip off pacer Pat Cummins, much to the disappointment of his team-mates.

Shafique has so far hit three boundaries and a six while Azam's knock has included seven boundaries.

Earlier, Haq and Shafique were all caution as it took them until the fifth over to score the first run, before off-spinner Nathan Lyon struck.

The in-form Haq, who scored a hundred in each innings of the drawn first Test in Rawalpindi, was trapped lbw for one as he failed to connect with a sliding delivery.

Earlier, Marnus Labuschagne was bowled off a sharp Shaheen Shah Afridi delivery for 44 to prompt skipper Cummins to call the innings to a close with first-innings century-maker Usman Khawaja, who was born in Pakistan, remaining 44 not out.

Australia are on their first tour of Pakistan since 1998, having previously refused to tour the country because of security fears.