The Scots may not have qualified for the World Cup but last year beat tournament hosts and favourites England to prove they were well capable of causing an upset.
Saturday's opener had been abandoned without a ball being bowled due to rain, but the teams had better luck with the weather second time.
Dimuth Karunaratne, the new Sri Lanka captain top-scored with 77 in a total of 322 for eight -- just his second fifty at this level and first since he reached the landmark against Scotland on the same ground back in 2011.
It was one of three fifties on the innings, including opening partner Avishka Fernando's maiden ODI half-century.
But both batsmen men dropped off Brad Wheal, Karunaratne at first slip on 13 and Avishka on 22 at mid-off.
Karunaratne received a third life on 36 when Calum MacLeod couldn't hang on to a sharp chance at midwicket off left-arm spinner Mark Watt.
Sri Lanka pace bowler Nuwan Pradeep then took four wickets as Scotland slumped either side of being set a rain-revised target of 235, needing 103 off seven overs, and were bowled out for 199.