Newcastle - Ole Gunnar Solskjaer admitted Manchester United are suffering a confidence crisis after Matty Longstaff marked his Premier League debut with the superb strike that gave Newcastle a shock 1-0 win on Sunday.
Solskjaer's side paid the price for their latest lethargic display as Longstaff bagged his first goal for Newcastle in the second half at St James' Park.
United are languishing just two points above the relegation zone in 12th place after their third successive league game without a win.
This was a wretched display from United, especially given the paucity of the opposition provided by a Newcastle team who had fared even worse in the opening weeks of the season.
"We're disappointed. We did lack quite a few key players but that's no excuse," Solskjaer said.
"Some of the boys lack a little bit of composure and we don't create enough chances to win a game of football.
"The first half was the sloppiest we've been. In the second half we dominated but we didn't create."
Alarmingly, United's only victory in their last five matches in all competitions came on penalties against minnows Rochdale in the League Cup.
While it is surely too soon for Solskjaer to face the sack, the beleaguered United manager goes into the international break knowing results must improve quickly.
"It's my responsibility. I need to sort their heads out. Young boys lacking confidence, they need some help from experienced players and staff," Solskjaer said.
"They're human and they want to do well. They need to see the results of their hard work and we're not getting those results so that's going to affect them."
United haven't won away from Old Trafford since beating Paris Saint-Germain in the Champions League in March.
They are winless in eight consecutive top-flight away fixtures for the first time since a run of 11 from February to September 1989.
Their haul of nine points after eight games is their worst tally at this stage of a top-flight campaign since the dark days of 1989.
Asked if United's rebuild was in danger of imploding, Solskjaer said: "It will take however long it will have to take. It's a journey we've started on and the culture is getting there.
"We've given ourselves a big uphill challenge to get among the top four. If you only work on sunny days you'll never get to your destination."
Newcastle are only one point behind United after their second win in nine matches in all competitions this season.
In his 400th game as a Premier League manager, Magpies boss Steve Bruce ended a run of 21 games without a win against the club he served with distinction as a player.
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Newcastle's last home game attracted their lowest league attendance for eight years, and their last away game - a 5-0 humiliation at Leicester - ranked as their heaviest defeat in four years.
But even at such a low ebb, Newcastle were able to put United on the back foot.
Newcastle-born Longstaff didn't take long to get into the swing of it on his top-flight debut, alongside his older brother Sean in midfield.
It was the 19-year-old midfielder who almost opened the scoring midway through the first half when his dipping volley beat United keeper David de Gea but cannoned back off the crossbar.
It took United until late in the first half to finally test Newcastle keeper Martin Dubravka through Andreas Pereira's long-range strike.
That one was easy for Dubravka, but he should have been picking the ball out of the net moments later when Harry Maguire headed wide from Ashley Young's corner, despite being unmarked no more than four yards out.
Newcastle finally conjured a moment of quality to break the deadlock in the 72nd minute.
Jetro Willems reversed course to put Maguire on his backside before teeing up Longstaff for a fierce low drive that flashed past De Gea from 20 yards to leave United in crisis.