Marnus Labuschagne and Steve Smith scored centuries together for the first time to help Australia take day-one honours in the second Test against Sri Lanka.

Cricket's odd couple have combined for their finest hour together, with Steve Smith and Marnus Labuschagne centuries putting Australia in control of the second Test against Sri Lanka.

On a dominant day for the duo, Labuschagne scored his first Test ton outside of Australia with 103 before Smith finished unbeaten on 109 with the visitors 5-298 at stumps.

Long regarded as Australia's best two batters, Friday incredibly marked the first time the pair have scored a century in the same innings together.

It came as the pair combined for a crucial 134-run third-wicket partnership, that took the day away from Sri Lanka at Galle and gave Australia the upper hand.

"Both of us felt like we'd left some runs out there for the last few Tests," Labuschagne said.

"So it was nice to to cash in when we got an opportunity.

"It's usually one of us getting out and one getting get a big score. It was really nice to spend some time together there.

"I can't remember the last time we batted together for a century partnership.

"But it was nice to be able to build that partnership and do it together and talk through it while we're out there."

Ravaged by COVID-19 in the lead up to the Test, Sri Lanka's spinners endured a difficult day with only debutant Prabath Jayasuriya having any real success with 3-90.

The left-arm orthordox spinner was the man to finally remove Labuschagne when he had him stumped, before getting Cameron Green lbw on the sweep for four and bowling Travis Head on 12.

But as a general rule Sri Lanka's spinners struggled for consistency with their lengths, offering up too many loose balls on a Galle wicket far friendlier for batting than in the first Test.

Combined, it allowed Smith and Labuschagne to take a far more traditional approach than the helter-skelter first Test on the same ground last week.

Smith in particular waited for errors in length, driving superbly through the covers and mid-on as Sri Lanka's inexperience showed.

His century marked his first since January 2021, when he brought up three figures against India at the SCG exactly 18 months to the day earlier.

Labuschagne meanwhile pulled and cut well, while also sweeping on length when the ball was pushed fuller.

"That wicket was a lot nicer to bat on and just trust your game," Labuschagne said.

"I had to make sure I adapted my game a bit and not go as hard as I would if the wicket was going big.

The story could however have been so different for Sri Lanka, had Niroshan Dickwella not fumbled a simple stumping to remove Labuschagne on 28.

At that point Australia were 2-78 after David Warner (5) and Usman Khawaja (37) went in the first session.

Labuschagne then proceeded to hit two boundaries off the next over as he began to capitalise on the error.

Dickwella eventually did the job 76 runs later when a Jayasuriya ball spun sharply past the bat, but by then the damage had been done.