Man-of-the-match Upul Tharanga's ODI best of 120 at Lord's on Saturday saw Sri Lanka get off to an impressive start with a 20-run victory.
Although Jayawardene said he was disappointed that Sri Lanka, after a rapid start, made 257 for nine from their 50 overs it was more than enough as England, shoddy in the field, collapsed to 66 for four.
Marcus Trescothick and Jamie Dalrymple both made 67 but England never looked like overhauling their opponents' total and finished on 237 for nine.
What made the defeat all the worse was that England had gifted Sri Lanka a mammoth 42 runs in extras, the most they'd conceded in a One-day international, surpassing the 41 Sri Lanka received in Delhi back in 1989/90.
Among that tally were 23 wides. Sri Lanka, by contrast, bowled just three.
It was a fine performance from Jayawardene's team, who earlier this month came from behind to draw their Test series with England at 1-1 after staving off defeat in the opener at Lord's in May.
And this latest win followed on from their two-run victory in Thursday's Twenty20 clash at the Rose Bowl.
"It's been a long tour for us and I'm glad the hard work the guys are putting in is paying-off," Jayawardene told reporters at Lord's.
"The way Upul batted, he showed a lot of character and maturity," Jayawardene added of the 21-year-old man-of-the-match and left-handed opener, whose hundred was his third at this level and first against England.
"He held the innings together and with the start we had I was disappointed we didn't get to 300. But the difference was the extras. Our guys were a lot more disciplined than England today."
And when they fielded Sri Lanka did not have to rely, as so often in the past, on off-spinner Muttiah Muralitharan. Instead pacemen Dilhara Fernando and Lasith Malinga took six wickets between them.
For England, without several first-choice players through injury, including captain Michael Vaughan and key all-rounder Andrew Flintoff, it was another poor performance in the run-up to next year's World Cup in the Caribbean.
In 2005, England won just eight of their 22 one-day internationals, while earlier this year they lost a one-day series away to India 5-1.
England coach Duncan Fletcher has often cited his side's lack of experience as a reason for their poor one-day form but at Lord's it was spearhead quick Stephen Harmison, with eight wides, whose radar was most off-target.
And when England batted, Trescothick excepted, it was 25-year-old Middlesex all-rounder Dalrymple, in only his second One-day International after making his debut against Ireland on Tuesday, who starred.
"Our extras were far more than you'd want in One-day cricket where games are decided by such small margins," said stand-in skipper Andrew Strauss.
"We know we're better than that and we'll be looking for an improved performance on Tuesday," the opening batsman added.
"The bowlers came back well but Sri Lanka were able to build-up some useful momentum in their first 15 overs, which given there was a little bit in the wicket was disappointing.
"Likewise with the batting, at the start of the innings losing too many early wickets put us under pressure. It was a disappointing day at the office for us and it's best not to dwell on it.
"But I'm still very excited about the players we've got," said Strauss, who paid tribute to county colleague Dalrymple.
"There's a lot of talent there. Jamie Dalrymple came through and showed everyone what he could do. He handled the big stage exceptionally well.
"He played the way an experienced batsman would and showed a lot of composure in the heat of the battle.
"If we'd lost two fewer wickets or so we could have chased that total. The onus and the responsibility is on the experienced players to put in perfomances when you've got a young side."