Usman Khawaja's century put Australia in control at the end of day one of the second Test against Pakistan at the National Stadium in Karachi.

After drawing last week's opening Test in Rawalpindi, it was Australia who laid down an early marker on Saturday as they reached stumps on 251-3.

The in-form Khawaja batted all day as he made an unbeaten 127, while Steve Smith was also on course for three figures before being caught by Faheem Ashraf off the bowling of Hasan Ali for 72 just before the close.

Khawaja profited from what he described as "pretty negative" bowling from the hosts to hit 13 fours and one six in a classy knock.

David Warner went for 36 and Marnus Labuschagne was run out on a duck, but Khawaja's batting ensured even the late loss of Smith did not hamper the tourists too much.

Nathan Lyon will resume alongside Khawaja on Sunday as Pakistan look to make inroads after a frustrating opening day.

"It would have been nice to have Smith there at the end," Khawaja said. "We've still got plenty of batting to come. 

"The wicket was pretty nice today and is going to get worse, and it's feeling like it'll break up in the back end of the match. 

"They bowled pretty negative and we were not going to give them free wickets. It would have been nice to get a hundred both in Rawalpindi and here but I'll take this one."

Khawaja goes one better

After falling three short of a century in Rawalpindi last week, the Islamabad-born Khawaja was not to be denied an 11th Test century on Saturday.

He has now logged two centuries and five half-centuries across eight Test innings against his country of birth.

Pakistan falter

Babar Azam's tactics after tea must be questioned, though Hasan did find a breakthrough when ending a 159-run partnership late on to give Pakistan a platform to build on.

Pakistan have only suffered two defeats at the National Stadium in 44 Tests and will need some quick wickets with the new ball in Sunday's morning session.