PAK vs AUS 2nd Test, Day 2: Usman Khawaja, Alex Carey power Australia to 505-8 in Karachi

Islamabad-born Khawaja's third century in four Tests included 15 fours and a six.

Usman Khawaja's marathon 160 and Alex Carey's career-best 93 helped Australia rack up 505 for eight against Pakistan on day two of the second Test on Sunday. It was a day of painstaking accumulation at the National Stadium where the Pakistan bowlers kept the run rate under check but only five wickets fell in three sessions for all their hard work under a harsh sun.

Usman Khawaja walks back to pavilion after his dismissal on 160 runs during 2nd day of second Test between Pakistan and Australia.(AP)

Mitchell Starc saw off 95 deliveries for his dour unbeaten 28 and Australia captain Pat Cummins was unbeaten on nought at the close.

"Tomorrow we'll see what the skipper does but it's great to have 500 runs on the board," Carey said.

"Hopefully, the pitch starts to deteriorate tomorrow and on day four and we can create those 20 chances. So the more runs we get now, the better position we'll be in if we have to bat again."

Earlier, after Australia resumed on 251-3, Shaheen Afridi subjected Nathan Lyon to a bouncer barrage but the nightwatchman did not flinch and went on the attack with the pull shot.

Lyon hit five fours in an entertaining 38 before he had his stumps rearranged by an express delivery from Faheem Ashraf, ending a 54-run stand with Khawaja.

Khawaja had shelved the reverse sweep on Saturday but Pakistan were convinced they had him caught in the slips when the opener attempted the shot against Nauman Ali.

However, replays ruled out any ball-bat contact and Pakistan lost a review.

Khawaja duly brought up his 150 but could not better his highest score of 174 as Sajid Khan dealt a double blow.

The off-spinner trapped Travis Head lbw for 23 and spun one past Khawaja's bat to hit the off-stump.

Islamabad-born Khawaja's third century in four Tests included 15 fours and a six.

Cameron Green, who was not even born when Australia last toured Pakistan in 1998, made 28 before Nauman confounded him with a sharp-turning ball that pitched outside leg stump and hit the off.

Carey swept well and Starc batted resolutely to frustrate Pakistan and take Australia past the 500-mark.

Pakistan captain Babar Azam brought himself on to bowl, partly to give respite to his overworked spinners, and struck in his first over.

In his haste to reach the 100 mark before close of play, Carey went for a slog sweep but lost his stump to a delivery from part-time spinner Babar that kept low.

His stellar knock included seven fours and two sixes.

Carey left the field to a standing ovation from his team mates after adding 98 runs with Starc for the eighth wicket.

"Our plan was to bowl stump-to-stump and not leak too many runs," Pakistan all-rounder Faheem told reporters.

"The pitch was slow. So even when we were getting reverse swing, their batsmen had enough time to negotiate it."