Steve Smith (64no) and new opener Travis Head (57) played supporting roles on day one, the former passing 10,000 Test runs and the latter vindicating the bold call to drop teenage opener Sam Konstas.
Steve Smith acknowledges the crowd after completing his 10,000 Test runs milestone. (AP PHOTO)
But after Australia won the toss, the first two sessions belonged to 38-year-old opener Khawaja, who fired back at those questioning his Test future during a middling home summer.
A jubilant Khawaja (119 no from 166 balls) brought up his 16th Test century and first since the 2023 Ashes by playing Asitha Fernando past fine leg for four on the 135th ball he faced.
The veteran's antics ensured Australia went to tea at 2-261 and seemingly in control on a Galle deck that is tipped to become trickier for the batters as the series opener goes on.
Usman Khawaja used the reverse sweep to telling effect in his undefeated innings. (AP PHOTO)
Once derided for his track record against spin, Khawaja looked comfortable from the outset, initially playing the steady hand next to a ravenous Head.
Shifted up from No.5, Head brought up his half-century in 35 balls - the equal sixth-fastest Test 50 by an Australian - before holing out to long on hunting his second six.Â
That was when Khawaja took control.
With limited bounce on offer, Khawaja rejoiced in bringing out the sweep shot and rode his luck as Sri Lanka missed three chances to take his wicket by tea.
He was dropped behind the stumps either side of lunch, with Sri Lanka also opting not to review a caught-behind chance that would have sent him packing on 73.
Captain Dhananjaya de Silva had earlier declined to take an LBW shout on Travis Head upstairs, only to watch on as ball-tracker revealed Fernando's delivery as plumb.
Sri Lanka would go on to burn a review on another LBW shout that sailed well wide of Head's stumps.
Marnus Labuschagne never looked comfortable in his brief innings of 20. (AP PHOTO)
The missed chances kept on coming even after Jeffrey Vandersay had Marnus Labuschagne (20) dismissed cheaply caught behind just before lunch.
Kamindu Mendis dropped a tough high chance on Smith at cover in the second session after Prabath Jayasuriya put the stand-in captain down from his own bowling when he was on one.
Only minutes earlier, Smith had joined Ricky Ponting, Allan Border and Steve Waugh as one of only four Australians to reach 10,000 runs.
A beautiful six down the ground towards the historic Galle fort, and three fours from the same Vandersay over were the highlights of Smith's fastest Test-half century, brought up from 57 balls.
The firepower could keep coming for the Australians after tea with spin specialist Josh Inglis coming in at No.5 for his Test debut.
Selector Tony Dodemaide told the touring Australian press that dropping Konstas to move Head to the top and bring Inglis had been a "difficult" call, made with Konstas's inexperience and Head's last subcontinent tour in mind.
Usman Khawaja (l) and Travis Head (r) got Australia off to a flying start. (AP PHOTO)
But the anxiety would have been short-lived as Head bludgeoned three fours from the opening overs in a sign of the brutal team batting performance that was to follow.
Australia named a spin-heavy attack at Wednesday's toss, with all three off-spinners Nathan Lyon, Matt Kuhnemann and Todd Murphy picked ahead of second front-line quick Scott Boland.
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