Pallekele - England beat Sri Lanka by 18 runs under the Duckworth/Lewis method in the rain-hit fourth one-day international on Saturday to take an insurmountable 3-0 series lead.
England captain Eoin Morgan won the toss and asked Sri Lanka to bat first with the hosts reaching 273/7 in 50 overs.
Dasun Shanaka made a run-a-ball 66, including five sixes, while Niroshan Dickwella scored 52. Moeen Ali took 2-55 for England.
England were 132/2 after 27 overs in reply when rain interrupted play. No further overs were bowled and England had done enough to win under the D/L method.
Jason Roy made 45. Joe Root and Morgan were not out on 32 and 31, respectively.
Spinner Akila Dananjaya took 2-27.
England secured the five-match series 3-0 with the first game being washed out.
Roy and Alex Hales - replacing the injured Jonny Bairstow - gave England a 52-run opening stand in nine overs before Hales (12) was stumped by Dickwella off Dananjaya.
Roy hit 45 runs off 49 balls before Sri Lanka won a leg-before review against him off Dananjaya.
Root and Morgan then shared an unbroken 56-run stand for the third wicket.
Earlier, England seamer Chris Woakes gave his team a promising start by removing Sri Lankan opener Sadeera Samarawickrama - caught by Jos Butler - with the total on 19.
Dickwella and Dinesh Chandimal added 70 runs for the second wicket before Chandimal was bowled by Ali for 33.
Dickwella's 52 included five boundaries and came off 70 deliveries.
Shanaka hit five sixes and four boundaries, while Thisara Perera was run out on 44.
The final match is at Colombo on Tuesday.