Jose Mourinho had responded to West Ham United's first and second goals with a certain composure, but as Marko Arnautovic added a third, he turned to his bench, incandescent and shouting indiscriminately, like a man losing control.
A few minutes earlier, Marcus Rashford had given Manchester United faint hope of salvaging a point from a truly wretched performance. Instead, the substitute's goal would be a consolation, and scant consolation at that after such a shambolic, dispiriting display.
It says everything about United's malaise that this result seemed a foregone conclusion after just five minutes, as soon as Felipe Anderson capitalised on a spell of near-total dominance for West Ham to open the scoring. Victor Lindelof's own goal would compound the misery of a dismal first half.
"I expect to win tomorrow. I expect to play very well tomorrow," Mourinho had said ahead of this game, but how could he truly have believed that? After a week in which his relationship with Paul Pogba deteriorated further, a week in which a mini-revival collapsed into a crisis, United increasingly look like a broken, divided team that could not buy a win.
The same could be said of West Ham a few short weeks ago, of course. A team that took no points from its opening four fixtures, that risked equally a club record of failing to score in three consecutive home matches, instead eased their way to their first league victory at the London Stadium of the season.
There were spells where Manuel Pellegrini's side utterly dominated United and the first of them produced the opening goal. The game was not yet six minutes old when Anderson deftly turned Pablo Zabaleta's low cross around David de Gea with a trailing leg, but even at that early stage, it was no exaggeration to say this breakthrough had been coming.
United had touched the ball just 25 times in those early stages, gifting their hosts more than four-fifths of possession and treating the halfway line as if it was a police perimeter. And yet, the only crimes committed were on their side of the line.
Mourinho's decision to use a three-man defence backfired, with young Scott McTominay's deployment on the right-hand side of the three particularly costly. The 21-year-old could be seen constantly turning his head in the opening minutes, desperately attempting to find his bearings in an alien position for this natural midfielder.
This lack of positional awareness would cost him. Replays of the opening goal suggested that Zabaleta had strayed marginally offside, though it would have been easier for the assistant referee to make the correct call had McTominay stepped up and kept in line with the rest of his defence.
To blame a young professional asked to fulfil unfamiliar role would be wrong when United's problems could be seen all over the pitch. Mourinho's side were devoid of any intensity, lacking any semblance of structure, until a handful of senior players began to take matters into their own hands.
Ashley Young, United's captain in Antonio Valencia's absence and following Pogba's demotion, was chief among them, and it was his cross from the right that Romelu Lukaku turned against the outside of the post for the visitors' first sniff of goal.
But despite United emerging from their early malaise, to call them competitive would have been a stretch at any stage, and the deficit was doubled as the interval approached.
Andriy Yarmolenko's strike was officially recorded as a Lindelof own goal, after a heavy deflection off the Swede took the ball out of De Gea's reach, but this was a collective failure rather than the fault of any individual.
Save Nemanja Matic, United's defence did not react to the breakdown of a corner, having allowed Issa Diop to mistime a free header from the set-piece itself. The deflection off Lindelof was cruel but in their tardiness to take the ball from Yarmolenko, United had mad their own luck.
Lindelof was sacrificed after United failed to show any signs of improvement in the second half's opening exchanges, with Rashford introduced and McTominay now part of a defensive two with Chris Smalling.
With only a Marouane Fellaini far-post header to show for their efforts over the subsequent quarter-of-an-hour, Mourinho moved again, removing Pogba and Martial to cheers from the home support. Rashford pulled one back once play resumed, flicking a corner around Lukasz Fabianski a la Anderson's opener.
It would not precipitate a United revival, however. Instead, came their nadir. Arnautovic was offside when Noble first took the ball, but the West Ham captain was under such meagre pressure, he had time to move back in line with Smalling and McTominay without being detected.
Before either of United's centre-halves knew it, Arnautovic had been effortlessly slipped through, was bearing down on De Gea and about to score his side's third. Mourinho then turned to his bench, shouting into the ether.
