George Dobell is a senior correspondent at ESPNcricinfo
England were 170 for 5. They required 63 more runs to win and they had five wickets and 70 deliveries in hand. Their remaining batsmen had 12 Test and 54 first-class centuries between them. They had one foot in the semi-finals.
But then Moeen Ali took a chance. He must have seen the fielder on the long-off fence, but he backed himself to clear him. Instead his lofted drive was well taken by Isuru Udana and Sri Lanka were thrown a lifeline. It was a dismissal that precipitated a slide in which four wickets fell for the addition of 16 runs. Suddenly something relatively simple was almost impossible.
We have to be a bit careful criticising England's limited-overs batting. You don't set the records they have - the total of 481, the 17 sixes in an individual innings, the 46-ball hundred - without taking a certain amount of risk. It would be unfair to praise that bold approach one day and decry it the next. It is absolutely inevitable they will fail sometimes.
But this was a run-chase. And a relatively small one at that. So there was no need for the high-risk strokes. Simple rotation of strike and calm heads would have sufficed. And, as admirable as England's bravery and aggression has been, you do wish it was combined with a bit of common sense just a little more often. Adapting to surfaces and situations is key to success across formats and this was Moeen's 100th ODI. With all that talent and all that experience, it really does seem fair to expect a bit better than this. It was, in its own way, just a little reminiscent of Kevin Pietersen's dismissal in the second innings of the Perth Test of 2013. And we all remember how that was received. One hopes Moeen did not whistle at any point afterwards.
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Moeen might claim, with some justification, that the wicket was challenging. So he might claim, with some justification, that if he could smash a quick 20 or so more runs, he could have put the game beyond doubt. But that's the logic of the get-rich-quick scheme; the mentality of the gambler. There was a simple single on offer here and Moeen, who had hit a six the previous delivery, showed a lack of composure in not taking it. It was a key moment in a defeat that puts England's World Cup progress in jeopardy.
To be fair, Jofra Archer's dismissal - caught at long-on - was every bit as grim as Moeen's. But he is a 24-year-old playing his ninth ODI. And he is batting at No. 10. Moeen is 32 now and playing in his second World Cup. More is expected of him.
Was it relevant that, the previous day, Moeen had spoken of the internal - and good-natured - competition within the England dressing room over who could hit the most and biggest sixes? It seemed a light-hearted chat at the time. And Moeen is no doubt right when he talks of the importance of keeping the environment light and positive. But just because you don't want them to over-think situations doesn't mean you don't want to think at all. And the balance here was more towards reckless than responsible.
It would be simplistic to single out one man for England's defeat, though. Just as it would be wrong not to acknowledge the fine performance of Sri Lanka. Angelo Mathews' innings raised some eyebrows while it was in progress - he had made 34 from 80 balls at one stage - but in retrospect it appears an intelligent contribution from a man who adapted to the conditions better than most on the home team. He gave his bowlers a chance and, with Lasith Malinga nailing every yorker and his team-mates providing decent support, it was a chance they grasped. This upset was every bit a result of Sri Lanka playing well as it was England playing poorly.
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But that doesn't mean England didn't play poorly. Or bat poorly, at least. It doesn't mean that Jonny Bairstow didn't play round a straight one or that Jos Buttler didn't waste a review having done the same. And if Joe Root - who was batting masterfully well - was a bit unfortunate to be caught down the leg side, the best sides don't trust to luck. They make sure.
And then there's James Vince. He did receive a decent ball that left him a little while inviting the drive. But it was an invitation he could have declined. Or at least an invitation he could have accepted with his foot to the pitch of the ball. As it was, that foot barely moved. It was a dismissal as soft as it was familiar.
What do England do with Vince? He continues to look a million dollars. But increasingly he appears to be the sports-car which spends more time with its bonnet up than its roof down; the beautiful partner who can't stop straying; the cigarette you'll regret in the morning. He promises pearls and delivers pewter.
He has now batted 10 times in ODI cricket with a top score of 51 (which came the first time he batted, back in July 2016) and 40 times in international cricket without making a century. And while it is true he has rarely enjoyed a run in the side - he has always been looking over his shoulder and never quite able to relax - that is the nature of much of professional sport. Jason Roy, by comparison, has passed 50 five times in his last six ODI innings. Suffice to say, his return cannot come soon enough for England. One wonders, too, if there is any part of the England management pining for a replacement opener with six ODI centuries. They have made their bed with Alex Hales, however, and must lie in it.
This defeat does not ruin England's World Cup hopes. Their fate is still very much in their own hands. Two victories from their final three games should ensure their progression; one might even be enough.
But it does make life much more tense than it might have been. And it might well compromise their chances of resting key players - especially the fast bowlers - ahead of the semi-finals. Their opposition in those next three games - Australia, India and New Zealand - are fine sides who will sense blood. England really have made life much more difficult for themselves.
Most of all, this result will do nothing to decrease the nerves in the England camp. And judging by the performances against Pakistan and Sri Lanka, those nerves are quite a factor.