Buoyed by Samuels' 94-ball 110 not out, West Indies got to 206 for 9 from their 36 overs, but, having had them at 105 for 6 before a 135-minute rain interruption, Sri Lanka had that total scaled down via the Duckworth Lewis method.
Kusal Perera top-scored with 50 off 47 balls in a chase of 190.
Sri Lanka had moved to 179 for 5 after 32 overs when rains came down again to end the match.
