Ireland lost by 79 runs to Sri Lanka in the first of this week's two one-day matches between the sides in Dublin.
The hosts had their opponents 95-5 and 176-8 but the momentum swung as Mendis and Nuwan Kulasekara hit 43 from the final 22 balls as Sri Lanka made 219-8.
Ireland were 5-2 but a 58 partnership between William Porterfield and Niall O'Brien gave their side hope, skipper Porterfield top-scoring with 37.
Ajantha Mendis took 3-26 from his 10 overs to help bowl out Ireland for 140.
(BBC)