The Australian batsman scored his first Test century of the summer to leave Sri Lanka chasing a further 499 runs to win heading into day four of their clash with Sri Lanka at Manuka Oval.

The mercurial left-hander's 101 not out (136) was a timely reminder of his ability as questions hover over Australia's make-up for a crucial stretch in English conditions.

Just as Khawaja and Mitchell Starc locked themselves in for a World Cup defence and an Ashes campaign, Marcus Harris' passport might not be enough to get him on the plane.

Khawaja had managed just 209 runs at 23.22 during the home summer in which many expected him to finally reach his potential following a match-saving effort against Pakistan four months ago.

With a stroke to deep backward square, the weight of the world was seemingly lifted off the 32-year-old's shoulders to mark his eighth Test century in front of 8397 in Canberra.

It was a fist pump fit for the occasion, with Khawaja brushing aside off-field drama surrounding his brother Arsalan's arrest to regain his Midas touch.

"It's a hundred for Australia so it meant a lot, it wasn't fun getting a duck in the first innings and feeling like you let your team down," Khawaja said.

"Not [feeling pressure] from the outside, only from anything I put on myself. I've had a tough summer, I've had a lot of stuff going on off the field which has made things a lot tougher.

"It's been really nice to have my wife Rachel around with me the majority of the tour, she's been awesome just to have her around to travel with me, she's been my rock throughout the whole thing.

"[The off-field drama] has been tough. It's something you don't expect to happen, my family is very close to me and I'm very close to my family, so at some level it made it tougher to go out, concentrate and execute my skills.

"It has been very taxing mentally, and that's why Rach has been great, just being around and trying to take my mind off things. I'm feeling a lot better now than I was a month or two ago, but it has been a tough couple of months."

Selectors know an in-form Khawaja is among Australia's top three batsmen - and he averaged an extremely healthy 52.50 during a county cricket stint last year to bolster his case.

Khawaja's return to the runs comes on a favourable batting track that saw Joe Burns, Travis Head and Kurtis Patterson all post first innings hundreds.

Burns missed out in the second dig (nine) but his day one breakthrough (180) has left fellow opener Marcus Harris vulnerable after he could only muster scores of 11 and 14 in Canberra.

The final four rounds of the Sheffield Shield will go a long way towards determining Australia's line-up for the Ashes, a prize they haven't won abroad since 2001.

As the bans imposed on Steve Smith and David Warner edge closer to lifting, Burns has a huge chance to put himself in the box seat for an opener's berth with a county showing around the corner.

Khawaja's return to form came against a second-string Sri Lankan attack but the Australian No. 3 can only score against who is in front of him.

Much like fast bowling spearhead Mitchell Starc can only claim the scalps of the batsmen at the other end of the pitch, claiming 5-54 for his first five-wicket haul since March.

The tourists folded for 215 in reply to Australia's 5d-534. Khawaja's ton steered the hosts to 3d-196, with Sri Lanka (0-17 chasing 516) now staring down the barrel of a loss inside four days.

Whether Sri Lanka have a full XI on hand for the run chase remains to be seen with Kusal Perera being monitored by team staff, having retired hurt in the first dig after being struck on the helmet.