De Silva, leading Sri Lanka in the absence of Arjuna Ranatunga, took three wickets for 12 runs off 10 overs with his fast off-breaks to restrict the ECB XI to a moderate total of 141 for 9 off 50 overs, and then hit an unbeaten 53 to steer his side home comfortably with nearly 22 overs to spare.
His previous contributions in the one-day game on tour are 82 for a World XI in the Diana memorial match at Lord's and an unbeaten 73 against Worcestershire at Worcester.
The pitch for the one-day contest which is serving as Sri Lanka's lead-up to the triangular contest starting on August 14, was a poor one. The surface was soft and it was not before long that the top layer started to come off. Although it didn't prove dangerous to the batsmen, it turned out to be unplayable against the spinners.
The ECB XI put into bat first by De Silva, knocked their first 48 runs at a gallop using up only six overs against the medium-pace of Mario Villavarayen and Suresh Perera, before the spinners strangled them. Niroshan Bandaratilleke, Upul Chandana and Russel Arnold, joined their captain in routing the ECB side which comprised Minor County players by taking all the wickets.
Contributing towards Sri Lanka's success was schoolboy wicket-keeper Prasanna Jayawardene, who brought off two smart stumpings and a catch on a difficult pitch.
Sri Lanka began their chase with Marvan Atapattu and Russel Arnold putting on 60 for the first wicket. But they were both dismissed within four runs of each other, and it was left to De Silva, who promoted himself in the batting to gain practice and Hashan Tillekeratne to see the side through, sharing an unfinished third wicket stand of 80.
Sri Lanka next travel to Northampton to take on Northamptonshire in two one-day games on Friday and Sunday.