The hosts, who won the previous two Tests by innings margins and plenty of time to spare, are firm favourites to secure their 10th successive victory over Bangladesh despite the threat of rain.
The tourists are under no illusion they can prevent a clean sweep. All they want to do is bat out the opening day if they are again given first strike on a pace-friendly Asgiriya stadium wicket.
Bangladesh were shot out for 89 and their lowest total of 62 on the opening days of the previous two Tests after being sent in to bat by Sri Lankan captain Mahela Jayawardene.
Bangladesh's young skipper Mohammad Ashraful, who turned 23 on Saturday, admitted he was worried by the way his team surrendered at the start of both Tests.
"Few teams have recovered after making just 89 or 62 in the first innings, so the big defeats that followed did not surprise me at all," said Ashraful.
"What hurt me is that all the batsmen went down in a heap. The entire top order has to click if we are to put up a reasonable score.
"It is not that the boys are not trying, or they do not know what is wrong, but nothing has worked for us on the first day."
Bangladesh managed 254 and 299 in the second innings of the two Tests to raise hopes that all is not lost against one of the most formidable attacks in world cricket, led by the prolific Muttiah Muralitharan.
Ashraful and teenager Mushfiqur Rahim softened the second Test defeat by their record partnership of 191 for the sixth wicket, Bangladesh's best ever in the 48 Tests they have played so far.
Ashraful made an unbeaten 129, his fourth Test century and the third against Sri Lanka, while the 18-year-old Rahim hit 80 in a splendid rearguard action at the P. Sara stadium.
Bangladesh have been let down by the poor performance of the two senior pros, former captain Habibul Bashar and left-arm spinner Mohammad Rafique.
Bashar, who was sacked as captain for this tour, gets a final chance to save his international career after making just 36 runs in four innings.
Rafique, just six scalps away from becoming the first Bangladeshi to capture 100 Test wickets, has managed just one wicket in the first two Tests at the cost of 272 runs.
Off-spinner Muralitharan, who took 14 wickets in the first two matches, begins his home town Test just 20 scalps away from equalling retired Australian spinner Shane Warne's world record tally of 708.
Sri Lanka will be without veteran seamer Chaminda Vaas, who has rejoined English county Middlesex after being given permission by Sri Lanka Cricket to miss the final Test.
Vaas is likely to be replaced by another left-arm seamer Sujeewa de Silva, while openers Michael Vandort and Malinda Warnapura may be retained even though Upul Tharanga is fit again after a heel injury.
The first two Tests escaped the monsoon rains, but thundershowers have been forecast in this hill resort on all five days of the Test.