De Silva and Dinesh Chandimal put together an unbeaten 188-run partnership for the sixth wicket to thwart the Australian bowling attack after Sri Lanka were reduced to 26 for five while batting first in the third Test.
De Silva continued his gritty innings by reaching 116 at close, with strong support from Chandimal, who scored his 11th Test half-century, batting on 64.
Australia's Mitchell Starc and Nathan Lyon shared five wickets between them to decimate the Sri Lankan top-order before lunch but failed to make further inroads in the remaining two sessions.
De Silva's 240-ball stay was laced with 16 boundaries while Chandimal has so far hit four boundaries.
The 24-year-old De Silva, who made his debut at the start of this series, survived a dropped catch on 104 by Shaun Marsh at cover with Starc being the unlucky bowler.
But the batting duo ensured Sri Lanka go into the second day with their tails up against the Australian attack that seemed to have lost its way after the initial burst.
The visitors had dominated the morning session with Starc striking early to have Kaushal Silva trudging back to the pavilion after a 15-ball duck.
Lyon, who had had been criticised for failing to utilise the turning conditions, also proved effective at the Sinhalese Sports Club ground with his two wickets.
The spinner seemed to have learnt his lessons on these pitches after getting Kusal Perera caught at first slip and then the prized wicket of Sri Lankan skipper Angelo Mathews, who was out for just one.
Starc also kept the other end busy with his wicket-taking as he bowled opener Dimuth Karunaratne for the fifth time in the series.
Sri Lanka, who took an unassailable 2-0 lead in Galle, have a great chance to register their first whitewash against a major team since gaining Test status in 1981.
Disclaimer: No Business Standard Journalist was involved in creation of this content
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