Sri Lanka beat Ireland by 79 runs to win the first one-day international at the Clontarf ground in Dublin on Tuesday.
After losing the toss, Sri Lanka made 219 for eight in their full 50 overs before dismissing Ireland for just 140 in reply with more than 10 overs to spare.
Man-of-the-match Ajantha Mendis starred with both bat and ball for Sri Lanka, hitting an unbeaten 18 off just nine balls before taking three wickets for 27 runs with his unorthodox spin.
Suranga Lakmal struck with the new ball on his way to three for 29 in an innings where Ireland captain William Porterfield top-scored with 37.
Sri Lanka had been in trouble at 95 for five before the lower order, with Nuwan Kulasekara making an unbeaten 42, got the tourists — without star batsmen Mahela Jayawardene and Kumar Sangakkara — to a total that proved more than enough.
The two-match series concludes at Clontarf on Thursday, with Sri Lanka then continuing their tour with limited overs and Test campaigns in England.