But, a 70-run partnership between Chamara Silva and Jeevantha Kulatunga revived the Lankan innings to take the score to 145. Upul Chandana and Sajeeva Weerakoon later shared an unbroken 103-run stand for the eighth wicket, which saw Sri Lanka set a victory target of 262.
Weerakoon top-scored with 53 off 60 balls, hitting four fours and one six, while Chandana's unbeaten 46 came off 62 deliveries and contained three boundaries.
Kulatunga's enterprising 40-ball 42 was studded with six fours and a six, while Chamara's 37 came off 58 deliveries with the help of four fours.
John Mooney was the most successful bowler for Ireland, claiming the wickets of Ian Daniel, captain Aviskha Gunawardene, Malinda Warnapura and Chamara Silva to finish with 4 for 43.
In reply, Ireland had difficulty to score freely and were shot out for 174 in 43 overs, with only captain William Porterfield (73), coming at number three, offering some resistance.
Weerakoon, who took two wickets also, was declared the man of the match.
This victory is Sri Lanka's first while a second successive defeat for Ireland.