Bojan Krkic took advantage of a terrible error by Memphis Depay to put Stoke ahead and Marko Arnautovic scored a 25-yard screamer as Van Gaal 's position came under even more scrutiny after going seven games without a win.
Do not be fooled by the 2-0 scoreline
This was a comprehensive win for Stoke, one that caused glee among the home supporters who branded United "boring" throughout.
"You're getting sacked in the morning," the home fans chanted when Arnautovic drove his fierce shot into the top corner and one Stoke fan dressed as a cross between the Grim Reaper and Jose Mourinho waved an oversized P45 in Van Gaal's direction.
With Mourinho on the market, and United looking like they have forgotten how to win - and play attractive football - Van Gaal's position is looking more precarious than ever.
The Dutchman, who dropped Wayne Rooney from his team for the first time, demanded an apology from the media for stories suggesting he would be replaced by Mourinho on Wednesday, but it is the 2,557 United fans who travelled to the Britannia Stadium on Boxing Day who deserve an apology for this latest sorry performance.
It was clear from the first whistle that Stoke had the hunger, desire and confidence United lacked.
There was a moment of panic when Jack Butland miscontrolled Arnautovic's poor back-pass while Anthony Martial raced at the Stoke goalkeeper, but the hosts cleared.
That was the first and last sniff of goal United would have in the first period.
Daley Blind and Ashley Young had no answer to the trickery and pace of Xherdan Shaqiri and Arnautovic.
Blind, still dizzy from taking a ball to the nose from Geoff Cameron, was turned inside out by Shaqiri, who was only stopped by an Ander Herrera foul
The Spaniard was doing little to justify his place in the starting XI and gave the ball away twice in the opening 15 minutes
When United kept possession, they did little with it
The Stoke supporters chanted "boring, boring, boring" every time United had the ball - and they were right
The visitors were woefully short of ideas.
When Stoke took the lead it came as no surprise
That it came about because of an embarrassing gaffe from a United player came as no shock either.
Depay, a £25million player who scored 22 league goals for PSV Eindhoven last year, tried - and failed - to head a simple ball back to David de Gea, Glen Johnson stole in and squared to Bojan, who tapped in.
The manner of Stoke's second goal was just as embarrassing for United
Ashley Young flung his right hand up in the air to block Arnautovic's cross
Kevin Friend awarded a free-kick, which Bojan took
His shot cannoned off the wall and fell to Arnautovic, who hit the fiercest of drives into the top corner.
Van Gaal looked on despondently
His mood would have darkened further had Arnautovic scored another when through on goal moments later but luckily for United, the Austrian shot wide.
Van Gaal brought Rooney on at half-time and the captain added energy and fight - he caught Philipp Wollscheid in the face with his forearm while jumping for the ball - but little quality.
Stoke, a club who just a few years ago were effectively branded a rugby team by Arsene Wenger, were still by far the better side
The Potters were toying with United.
When the ball went out of play for a Stoke throw, Mark Hughes demanded it be returned quickly
He did not want to settle for 2-0
He wanted to inflict a real hammering on his old employers.
There was a brief glimmer of hope for Van Gaal when Rooney squared for Marouane Fellaini, but the Belgian scuffed his shot and Butland saved
There was no way back for the visitors.
TWEET OF THE MATCH
@rioferdy5: "I'm not even surprised....that's what hurts even more at @ManUtd ....come on boys" - former Manchester United defender Rio Ferdinand was not impressed with the club's latest performance.
https://twitter.com/rioferdy5/status/680739456857567232
PLAYER RATINGS
MANCHESTER UNITED
David de Gea: 6
Ashley Young: 4
Phil Jones: 5
Chris Smalling: 5
Daley Blind: 4
Michael Carrick: 5
Marouane Fellaini: 4
Juan Mata: 4
Memphis Depay: 3
Ander Herrera: 3
Anthony Martial: 4
Substitutes:
Wayne Rooney: 4
Andreas Pereira: 5
STOKE
Jack Butland: 8
Glen Johnson: 7
Ryan Shawcross: 8
Philipp Wollscheid: 7
Erik Pieters: 7
Glenn Whelan: 6
Geoff Cameron: 7
Xherdan Shaqiri: 8
Ibrahim Afellay: 7
Marko Arnautovic: 9
Bojan Krkic: 9
Substitutes:
Marco van Ginkel: 6
Mame Diouf: 6
Charlie Adam: 5
STAR MAN
Marko Arnautovic: Stoke caused United troubles across the final third all afternoon and no one did as much damage as Arnautovic
The forward occupied all three positions behind Bojan Krkic at various times in the match
He was too strong for United's defenders, who bounced off him when he ran with the ball
He picked United apart when he lifted his head up and took his goal superbly well.
MOMENT OF THE MATCH:
Arnautovic's goal
A late contender for the best goal of 2015 - the Austrian showed superb composure to steady himself when the ball dropped to him after Bojan's shot was blocked and he rifled the ball into the top corner from 25 yards to make it 2-0
David de Gea had no chance.
VIEW FROM THE BENCH
Van Gaal's position looks more precarious than ever thanks to this defeat
United are now without a win in seven matches and Van Gaal has some questions to answer
There was a plethora of top-quality international players on the pitch at Stoke, but none of them performed
Wayne Rooney may have been poor this season, but dropping your captain for such a big game was ultimately a mistake
Stoke boss Mark Hughes, on the other hand, rightly identified the full-back positions as United's weak spot and exploited that to perfection, with Arnautovic and Xherdan Shaqiri both causing Daley Blind and Ashley Young no end of problems.
MOAN OF THE MATCH:
Diving: Anthony Martial feigned a trip looking to earn a penalty in the first half
Referee Kevin Friend did not fall for it and ordered the Frenchman to get up
The official did not book Martial, but he had his yellow card out of his pocket after the break when Bojan went to ground in the United box without being touched
The striker did not appeal for a penalty, but it was clear what he was trying to do and deserved his booking.
WHO'S UP NEXT?
Everton v Stoke (Barclays Premier League, Monday, December 28)
Manchester United v Chelsea (Barclays Premier League, Monday, December 28)
Van Gaal said his players had not performed in the first half.
He told Sky Sports 1: "My thoughts are that we don't dare to play football in first half
We gave a very bad goal away and then they score out of a free-kick indirect.
"At half-time we have spoken with each other and I have to say the second half was much better but still we have created one or two chances and then you have to score and then maybe the belief is coming back
In the second half we played better but the problem is we don't dare to play and that's my analysis
"I'm always very faithful and I see also how (the players) have trained so they want to perform well but the circumstances are difficult, not only the wind but also with the pressure and that's why, in my opinion, we don't dare to play football
Second half we were in a losing position and we can give everything more easily and that we have done but then you have to score the first chance."
When asked if he was the man to help United rediscover their form, he said: "It's more difficult because I'm also a part of the four matches that we have lost
People are looking at me and I have to deal with that, but much more important is that the players have to deal with that because they have to perform."
And on his future he added: "It's another situation
We have lost the fourth game so you have to wait and see."
Source : PA
Source: PA