Kamindu Mendis hit a maiden ODI century and in-form Pavan Rathnayake scored 77 to guide Sri Lanka to 325-8 in the tri-series final against Pakistan in Lahore on Saturday.
Kamindu scored 131 off 128 balls and was ably supported by Rathnayake after Pakistan won the toss and sent the tourists in to bat on a slow-paced Gaddafi Stadium pitch.
The pair added 146 runs for the third wicket before Pakistan skipper Shaheen Shah Afridi dismissed Kamindu and Dasun Shanaka (17) in the space of two overs.
Kamindu and Avishka Fernando (38) helped set Sri Lanka up for a big total as they shared an opening stand of 87 inside 18 overs.
Spinner Salman Agha, who took 2-44, provided Pakistan with a double breakthrough, getting rid of Fernando and Kusal Mendis (8).
But Kamindu anchored the innings, hitting 12 fours and two sixes, improving on his previous highest ODI score of 64.
Pakistan pulled it back in the last five overs, taking three wickets for just 38 runs to stop Sri Lanka from posting a larger total.
Shaheen finished with 2-50 while Haris Rauf and Naseem Shah also took two wickets each.
PAKISTAN: Maaz Sadaqat, Fakhar Zaman, Babar Azam, Saad Baig (wk), Salman Agha, Hasan Nawaz, Arafat Minhas, Faheem Ashraf,Shaheen Shah Afridi (capt), Naseem Shah, Haris Rauf.
SRI LANKA: Kamindu Mendis, Avishka Fernando, Kusal Mendis (capt, wk), Pavan Rathnayake, Sahan Arachchige, Janith Liyanage, Dasun Shanaka, Dunith Wellalage, Maheesh Theekshana, Asitha Fernando, Dilshan Madushanka.