Jos Buttler sat on his own in the row of seats outside England’s dressing room, above the sightscreen at the southern end of the Wankhede Stadium. He wore the thousand-yard stare of a man who knew that, while his side are mathematically still alive in this World Cup, there is surely no way back from here.

As Buttler contemplated what had gone before, Mark Wood and Gus Atkinson had a swing, thrashing 70 runs off 5.3 overs. But even that partnership was not enough to save England from the ignominy of their biggest-ever defeat in men’s ODIs – that too on a night that they had earmarked as the game that would turn their World Cup around.

This was their third defeat out of four at this tournament, and all three have stung. They were swept aside by New Zealand in Ahmedabad and dealt with by Afghanistan in Delhi, but this was an utter meltdown in Mumbai. South Africa did not just beat England’s world champions: they made them look like a broken team.

It had the sense of the night when England’s title defence fell apart. They placed their hopes in the core of players who have underpinned their white-ball revolution and their rise from also-rans to double world champions; collectively, they have simply not performed.

There was a short passage towards the end of South Africa’s innings in which England exerted a brief sense of control. After 41 overs, South Africa were 264 for 5 and had not scored a boundary for 29 balls; Marco Jansen, their No. 7, had 11 off 19. “We could have looked like restricting them to 340 or 350,” Buttler reflected.

Instead, they managed 399. Heinrich Klaasen’s hitting was as crisp as it was clean as he swung his way to a 61-ball hundred, while Jansen pummelled 64 off his final 23 balls. “It spiralled out of control,” said Matthew Mott, England’s coach. “We were under siege for a while: Jos was looking around to see who was fit to bowl.”

England were simply exhausted, and not for a lack of basic fitness. “It certainly looked a bit like a warzone there at times,” Mott said. The problem stemmed from Buttler’s choice to bowl first when he won the toss, a decision he explained by saying: “[This is] generally a good ground for chasing, so that’s the reason behind it.”

But like so many decisions England have made in this World Cup, the explanation relied more on the past than the present and the future. England wandered out to field at 2pm, when Mumbai’s heat and humidity were at their most oppressive. It was a simple recipe for disaster: 11 Englishmen, left in the pan for four hours until fried to a crisp.

The evidence underlying Buttler’s assertion was scant. Chasing teams had a 75% win record in men’s ODIs at the Wankhede over the past decade, but the sample size was all of four matches. There is a strong chasing bias in the IPL, but the physical requirements of 90 minutes in the field in the evening are hardly comparable to a full afternoon in the blazing sun.

And if England were once a chasing team, they are no longer that side. This was their seventh loss in their last eight completed ODI run-chases; the only target they have hauled in was 210 on a turning pitch in Mirpur. England used to make light of scoreboard pressure; now, it inhibits them.

The conditions were brutal, not least for an XI which featured only three players under the age of 32. There was a revolving door of players coming on and off the field due to niggles, cramps or illness, to change their sweat-drenched shirts or simply for a moment’s respite. England’s medical staff became the busiest men in Mumbai.

Reece Topley was struck on his index finger in his fourth over, a suspected fracture which looks likely to rule him out of the tournament. Adil Rashid battled an upset stomach, which left him doubled over on the boundary. If it could have gone wrong for England, it did.

David Willey, one of the fittest men in their squad, described himself as England’s “donkey” last month due to his workhorse qualities; by the start of his ninth over, he was cramping so badly that he had to pull out of his run-up, before sending down a waist-high no-ball that Klaasen sliced for six.

And barely 90 minutes after walking off the field, Willey was back out in the middle. Four days after Mott had insisted England would not make “wholesale changes”, they made three: Sam Curran, Liam Livingstone and Chris Woakes were replaced by Willey, Gus Atkinson and Ben Stokes.

It left them relying on their top six to score the bulk of their runs, instead they managed 55 between them. Chasing 400, England “needed everything to go perfectly”, in Buttler’s words. Nothing did: it was game over after the first ball of the sixth over, when Marco Jansen had Dawid Malan strangled down the leg side to leave them 24 for 3.

England have not officially been eliminated from this World Cup, but the manner of this defeat was so painful that it is hard to see how they can turn things around. They talked a good game in Mumbai this week but, as they prepare to play Sri Lanka in Bengaluru on Thursday, the same messaging will have little effect.

Teams are likely to need six wins out of nine in the group stage to reach the semi-finals: England will need five in a row to reach that point, and do not look like they know where even one is coming from. “We’ll keep the belief,” Buttler insisted, but few outside of their dressing-room will join them – and those doubts must be seeping inside it.