Having clinched the five-match series a game ahead of time in Kandy on Saturday, the tourists were clattered all around Colombo to close on a humbling note.
This was no regulation loss, rather it was the kind of loss that sends the statisticians scrambling for amendments.
Sri Lanka’s 366-6 was their highest-ever total against England, by the small matter of 42 runs, and the final margin of victory was also without peer.
When the increasingly predictable thunderstorms hit England were sinking fast at 132-9, bad enough for a monumental 219-run loss on the Duckworth-Lewis-Stern method.
Morgan had sat out the game, resting to allow Sam Curran a rare outing, but emerged after play to insist the result would not be brushed under the carpet.
“Today we were put under serious pressure and we didn’t have a lot of answers,” he acknowledged.
“We didn’t take our game forward and there were actually areas it went backwards. Our fielding was extremely poor, our attitude was very poor and that has to be addressed. We’ll have to break down everything from yesterday’s practice – did we do too much? Did we overcook ourselves?
“We might have been a little bit fatigued, I don’t know, but we will break it down and find an answer because otherwise we’re just papering over the cracks which is not what we want to do.”
In the absence of the in-form Morgan, England’s batsmen folded badly at the Premadasa Stadium with Ben Stokes’s 67 the only real note of resistance despite his battle with cramp.
But the tone was set in the first innings, when a reshaped bowling attack featuring a fresh new-ball attack of Curran and Mark Wood, backed up by the returning Liam Plunkett, was torn apart.
Morgan plans to pick the bones out of 50 disheartening overs and come away with valuable experiences.
“You want to see the players who come in be challenged and put under pressure and that’s one thing we definitely saw,” he said.
“People will say you don’t want to see your bowlers hit all over the place, hit back over their head, but I think it’s necessary to learn. When we go into the World Cup and play against the better teams they perform like that on a regular basis.
“It’s not that you want to get used to it but you want them to get used to the situation.”
Head coach Trevor Bayliss added: “We learned that if we take our foot off the gas then this game can bite you on the backside, and certainly it did tonight.
“Sri Lanka outplayed us in every department, they were a lot better bowling, a lot better fielding and batted extremely well.”
He also pinpointed the fielding as a particular area of concern, with at least three dropped catches proving costly.
“I think fielding is an attitude. Unfortunately tonight, I saw a number of times where it looked like we weren’t really on the ball,” added Bayliss. “We were a few steps behind where we should have been, whether that’s concentration or whatever, we’ll have a chat after this.”
The tourists may be deserved world No 1s and on their finest ever run of results in limited-overs cricket, but this crushing in Colombo was an unwelcome throwback to darker days.
Niroshan Dickwella and Sadeera Samarawickrama piled on 72 in a bruising 10-over powerplay and continued taking all-comers on their way to a buoyant opening stand of 137. The pitch was looking flat, but so were England, whose middle-overs enforcer Plunkett was unable to put a lid on Dickwella’s ebullience.
When the breakthrough did come in the 20th over even the umpires needed to double check, with replays required to confirm Moeen Ali’s delivery grazed off stump after beating Samarawickrama (54).
Moeen also managed to prise out Dickwella, who looped a simple catch off the toe end after moving within one sturdy blow of a third ODI century.
By then Dinesh Chandimal (80) had already been dropped twice in single figures, by Tom Curran at long-off and Wood diving forwards in vain.
It proved costly, as he joined with Kusal Mendis in a stand of 102 in 76 balls. Chandimal was livelier than usual, not least when reverse-sweeping Adil Rashid into the stands, but it was Mendis who hit a new gear with six maximums in his 56.
It was apparent at the turnaround the chase would need to be a record one, England’s biggest ever by 17 runs, but Sri Lanka needed just 10 balls to extinguish hope.
Kusan Rajitha got the ball rolling by toppling Jason Roy with a textbook yorker and Dusmantha Chameera followed up by taking Alex Hales’s edge with a full, swinging delivery. Samarawickrama flung himself into a fine catch to complete the job.
If Jos Buttler was watching he did not heed the lesson, prodding at a near identical delivery two balls later for a matching duck.
At four for three, England were playing for dignity. Joe Root’s dismissal for 10, carving Chameera to point, made even that look a long shot.
The game was crying out for a counter-attack and Stokes hit 12 boundaries in his 67. He and Moeen (37) saw England past three figures, but it was all in vain, with only the cracks of lightning denying Sri Lanka all 10 wickets.