The batsman-wicket-keeper finished 100 not out, from 107 balls, with seven boundaries as the tourists continued their impressive comeback after being outplayed in the first two Test matches in England before rain helped them to a draw at Lord's on Monday.
Chandimal received good support in partnerships of 82 with Kusal Mendis, 89 with captain Angelo Mathews (49) and Dasun Shanaka, who hit 42 from just 19 balls, dominating the sixth wicket stand of 60.
Shanaka, on his ODI debut, crashed five fours and three sixes in an impressive display of hitting as the Ireland bowlers wilted under the onslaught.
Barry McCarthy, the one Ireland debutant, had made the breakthrough in the eighth over, having Danushka Gunatilake caught at slip with his second ball and he followed up with the first ball of his next over, holding a return catch to dismiss Kusal Perera.
But that only let in Chandimal and he was quickly into his stride, although it was Mendis who found the boundary four times in succession to quickly show McCarthy the other side of international cricket.
Mendis gave a difficult chance to Paul Stirling at slip on 43 but immediately after bringing up his fifty from 57 balls he gave a return catch to Kevin O'Brien, who proved the most accurate and economical of the Ireland bowlers.
Boyd Rankin, in his first home match for Ireland since his return from England duty, also bowled well to finish as the most successful bowler with two for 45.
Ireland did well to restrict the Sri Lankans to just 23 in the last three overs but the tourists were favourites to defend their imposing total.