Chandima made 100 from 107 balls as the tourists finished on 303-7.
Ireland were 164-4 when the rain came down, but after three overs were lost they never threatened to reach a Duckworth-Lewis revised target of 293.
They were bundled out for 216 as Dasun Shanaka finished with 5-43, having earlier clubbed a quickfire 42.
Barry McCarthy took two wickets in as many overs to restrict Sri Lanka to 48-2 after the powerplay, but Kusal Mendis led the recovery with a half-century before being caught and bowled by Kevin O’Brien.
Chandimal anchored the innings, hitting just six fours, as Angelo Mathews (49) and shanaka provided the pyrotechnics, with the latter firing 42 off only 19 balls prior to being bowled by Boyd Rankin.
Between them, Mathews and Shanaka hit nine fours and five sixes – the only maximums in the Sri Lanka innings.
Ireland’s reply got off to a strong start, but Shanaka bowled Paul Stirling for 27 after a 53-run opening stand.
The seam-bowling all-rounder then had Ed Joyce and John Anderson caught behind cheaply, and when skipper William Porterfield fell to Shaminda Eranga for 73, Ireland had fallen well behind the required rate.
O’Brien hit three sixes in making 64 from 49 balls either side of the rain delay, but he was trapped lbw by Nuwan Pradeep as the last six wickets folded for 18 runs, with Shanaka doing most of the damage.
The two sides meet again at the same venue on Saturday before Sri Lanka return to England for a five-match ODI series. (Courtesy BBC Sports)