Coetzer (right) and Cross put on an opening partnership of 201 runs
Sri Lanka suffered a humiliating seven wicket defeat against Scotland in a tour match played in London on Sunday.
Kyle Coetzer and Matthew Cross hit centuries in a massive double century partnership to chase down what looked like a modest 287 on a placid batting track.
Chasing a 50-over target of 287, captain Coetzer made 118, while his opening partner Cross finished unbeaten on 106 in the 42nd over in Beckenham.
Sussex bowler Stuart Whittingham picked up three wickets on his Scotland debut.
However, it will not be marked as a first win over full member opposition since the County Ground does not have one-day international status.
"It's a massive step forward for Scottish cricket," Cross said after making his highest score in international colours.
"It was a convincing victory against a side with plenty of Test match experience.
"We dominated and ran out comfortable winners."
Con de Lange was the other not out Scottish batsman on 19, while Callum McLeod (2) and Richie Berrington (19) added to the winning tally of 291.
Coetzer's 118 came from 84 balls, with Cross adding: "Kyle made it look easy. He took all the pressure off me."
Dinesh Chandimal top-scored for Sri Lanka on 79, with Chamara Kapugedera reaching 71 from 50 balls and opener Kusal Perera making 57.
Alasdair Evans joined Whittingham in taking three wickets, with Chris Sole bagging a brace, while 24-year-old wicketkeeper Cross made it a day to remember with four catches behind the stumps.
The teams meet again at the same venue on Tuesday.
Sri Lanka are warming up for the Champions Trophy, held from 1-18 June, where they will play India, Pakistan and South Africa in Group B.
Sri Lanka 287 all out (49.5 overs): Chandimal 79, Kapugedera 71, Perera 57; Whittingham 3-56
Scotland 291 for 3 (42.5 overs): Coetzer 118, Cross 106 no