Skipper Michael Vaughan admitted England were totally outplayed after Sri Lanka's 10-wicket romp in Dambulla.
The hosts raced to an overwhelming victory inside 14 overs after dismissing England for just 88, their second-lowest score ever.
"I didn't expect it to be as tough as it was today," Vaughan admitted.
"We didn't post a total and they came out and played in a positive manner. Full credit to the Sri Lankans - they were exceptional today."
LOWEST ENGLAND ODI TOTALS
86 v Aus at Old Trafford, 2001
88 v SL at Dambulla, 2003
89 v NZ at Wellington, 2002
93 v Aus at Headingley, 1975
94 v Aus at MCG, 1979
Vaughan estimated England were competitive for five minutes before Sri Lanka asserted, but promised an improved performance in the second match in Colombo on Friday.
"We didn't come out of the blocks at all. We were in it for about 1.2 overs, but we lost wickets at every interval," he said.
"It's not a great start to the series but we'll regroup and make sure we don't put in a bad performance on Friday."
Sri Lanka captain Marvan Atapattu said everything went to plan after he lost the toss.
Vaas's figures of 3-15 won him Man-of-the-Match honours
"You can't ask for anything more," Atapattu said after Sri Lanka won their first match following a four-month absence.
"I'm sure the break has done us some good, although we hadn't had a chance of playing together as a unit but all seems to be okay."
Expert catching highlighted Sri Lanka's effort in the field, with Mahela Jawardene taking two memorable one-handed gems in the slip cordon.
Atapattu added: "We have always been a good fielding side but we had a few lapses in the recent past. But we have worked hard at it."
Sri Lanka's debutant pacemen Nuwan Kulasekera and Dinusha Fernando claimed two wickets each, but Chaminda Vaas earned the Man-of-the-Match award with three scalps.
The left-armer said it was Sri Lanka's plan to bat first had they won the toss.
"It was a good toss to lose," Vaas admitted.
"Myself and Dinusha bowled well in the first 15 overs, and Kulasekera as well.
"The conditions were good for bowlers, so I'm happy with the way I and the two newcomers bowled."