Reports earlier in the day suggesting that Mourinho would be sacked with another poor result became even more relevant when Newcastle stunned their hosts with two goals in the opening 10 minutes.
Find out how all of the action unfolded courtesy of Sports Mole's minute-by-minute updates below.
Ironically, 'united' is the last word you would use to describe either of these two clubs at the moment, with today's hosts dogged by reports of dressing room fallouts and the visitors still under the ownership of the unpopular Mike Ashley.
They are two sides in desperate need of a victory, so let's start by looking at the teams the managers have selected in their bid to get one today...
Well, there is plenty to talk about regarding the Manchester United selection, with the headline being that Alexis Sanchez misses out once again, having also been dropped for last weekend's visit to West Ham United.
The Chilean did return for the Champions League game in midweek but was once again ineffective, extending his wait for a goal this season. He is replaced in the starting lineup today by Anthony Martial - as he was against West Ham too.
Romelu Lukaku completes the front three and will be bidding to end a five-game goal drought against a team he has a good record when facing in the past - namely directly contributing to 10 goals in 10 Premier League appearances against the Magpies.
On that occasion McTominay slotted into a back three - and was described after the match as United's best defender by Mourinho - but he is expected to play in a more familiar midfield role today.
Pogba is not the only player to have reportedly fallen out with Mourinho, though, and one of the others to do so - Antonio Valencia - is absent from the squad entirely this afternoon.
Eric Bailly continued at the heart of the defence, meanwhile, with Lindelof only making the bench and Jones once again left out of the squad completely.
Muto will be handed support by Ayoze Perez, who will play in the hole just behind the Japanese striker, but neither of them have scored a Premier League goal yet this season.
Dummett remains sidelined, though, which means that Javier Manquillo comes into the starting lineup in place of Kenedy, who switches forward to a more familiar attacking position.
Shelvey and Diame will patrol the middle of the park and could be crucial to any success for Newcastle if they are able to keep the likes of Pogba from exerting his influence on the game.
Debate continues to rage about whether it is the players or manager Jose Mourinho who are most at fault for the club's current form, but one this is for certain - they cannot afford to let it carry on for much longer.
Mourinho's side come into this match without a win in their last four games across all competitions, with that poor on-field form only adding to the relentless reports of unrest behind the scenes too.
The speculation over Jose Mourinho's future at the club continues to grow as a result, with the likes of Zinedine Zidane and Mauricio Pochettino having been tipped as possible successors.
This time around Mourinho's side have 10 points from seven games, leaving them already nine behind Manchester City and Liverpool.
Indeed, it took them 18 games to ship 12 goals last season, and considering that matches against Chelsea and Everton - in addition to a Champions League showdown with Cristiano Ronaldo's Juventus - are to come after the international break, that is something they need to improve on.
That was almost two months ago now - a four-game drought which includes draws with Wolves and Valencia in addition to their EFL Cup exit. United have only gone five home games without a win on one occasion since 1999.
Jose Mourinho on Newcastle: "Very, very, very good coach, a team that is always very well organised against especially the teams of the first part of the table, where their manager is very bright on his analysis of the opponent's qualities.
"The results they had against the top teams didn't get them points yet this season but gave them very, very close results and [were] very difficult matches for the opposition, so we expect a difficult match."
Newcastle United manager Rafael Benitez: "In all my time in England, I don't remember any fragile Manchester United team.
"All of them have been really strong every year with good managers, good players, so I don't see any fragile Manchester United team.
"I can see a team that everyone was expecting to be higher, but it's a question of time, like us. Who is at the top of the table in the Premier League? The three teams who spent more money than anyone.
"Who is at the bottom of the table? Teams that didn't spend so much money. That is a normal situation."
However, while the hosts are in poor form, Newcastle are in even worse shape and the supporters will have very little sympathy for the current Man United plight on and off the field having been through far worse in recent years.
Cardiff and Huddersfield are the only other teams still searching for that elusive first victory, although the Terriers' draw with Burnley in a 3pm kickoff means that Newcastle will begin this game in 29th place.
You have to go back to 1898-99 for one of those - a 10-game winless run at the beginning of the season - and the only other time that they have waited eight top-flight matches for victory was in 2015-16.
Six of those opening eight games - including today - come against teams that finished above them last season, and it is perhaps no surprise that their only two points of the campaign so far have come against the only sides they have faced who finished below them - promoted Cardiff and Crystal Palace.
The Magpies' next four games after the break come against Brighton, Southampton, Watford and Bournemouth - all of whom finished below them last season.
Goalscoring has been one of the main problems for Benitez's side, as they have failed to find the back of the net in their last two games and have not scored more than once in any match so far this season. Indeed, they have attempted just 52 shots this season with only 18 on target - both league-low tallies.
The home side's current troubles make this a very intriguing match, and against almost any other team it could be enough to tilt the match in the favour of the visitors. However, Newcastle have a woeful record here and are in trouble themselves, so I am going to go for a home win.
SPORTS MOLE SAYS: Manchester United 2-0 Newcastle
Well, the Magpies have won just one of their last 36 visits to this stadium to face United, losing 26 of those in a run which stretches back to 1972. The solitary win in that time came in December 2013, when Yohan Cabaye scored the only goal of the game against David Moyes's United.
Home and away, United have only lost three of their last 29 Premier League meetings, although one of those did come in their very last clash in February.
Newcastle were able to hold on to the lead on that occasion, but that is not something they have always done in this fixture. Indeed, they have lost seven Premier League games against United when scoring first - just one short of the competition's record for one club against another.
MAN UTD STARTING XI: De Gea; Young, Bailly, Smalling, Shaw; McTominay, Matic, Pogba; Rashford, Lukaku, Martial
NEWCASTLE STARTING XI: Dubravka; Yedlin, Lascelles, Fernandez, Manquillo; Ritchie, Shelvey, Diame, Kenedy; Perez; Muto
One through ball slices the United defence open and is collected by Kenedy, who is allowed to cut onto his left foot by Young and then curls his finish into the bottom corner past De Gea!
It is more terrible defending from the hosts as Muto collects the ball with his back to goal and is allowed to escape Bailly, turn and hammer his finish past De Gea. It is close to the United keeper, but there was such power on the shot that he could not keep it out.
1 - Newcastle United have taken the lead in a Premier League game for the first time this season. Unfamiliar. #MUNNEW— OptaJoe (@OptaJoe) October 6, 2018
Lukaku drifts out to the right flank and cuts onto his left foot before delivering a peach of a cross into the box. Rashford stretches every sinew to get there, but puts his header wide of the target when he should have scored.
A poor clearance from Smalling only falls as far as Kenedy, who nods it back into a dangerous area. Muto helps it on its way from close range, but De Gea pulls off a brilliant reaction stop to deny the striker a second goal. The ball almost escapes his grasp and creeps in, but he gathers it just in time.
Newcastle lead Manchester United 2-0 at Old Trafford, with both of those goals coming in a remarkable opening 10 minutes. The hosts are in dire straights at the moment and it is hard to see a way back for them at the moment.
Kenedy latched on to a through-ball which beat the entire United defence before easily taking it past Young and curling a pinpoint finish into the bottom corner.
This time it was Muto who got the goal, and again it was poor defending as he was allowed to turn inside the area before drilling his finish past De Gea.
Mourinho took Bailly off in favour of Juan Mata after the two early goals, and Scott McTominay has struggled since being forced to play at centre-back. The hosts need a drastic response in this second half.
Fellini collects a corner on his chest before teeing up Pogba, who drilled effort takes a nick on the way through. Dubravka reacts well to get down and save it, but he can only parry it into the path of Matic. It falls to the midfielder on his left foot and he has most of the goal to aim at, but he blazes his rebound well off target.
Mata lines up the free kick and curls it over the wall and into the bottom corner, with Dubravka unable to get across to it. Huge goal for United, giving them a lifeline here.
It is Sanchez who gets his first of the season in timely fashion, planting his header past Dubravka from just behind Martial. Sanchez was out of favour at the start of the match, but now he is the toast of Old Trafford!
It cannot be stated just how big that win could prove to be for Mourinho, who looked to be a dead man walking when United went two down inside 10 minutes. However, his players finally showed some fight and determination in the final 20 minutes and in the end they pulled off a result which could be the catalyst to kickstart their season.
Thank you very much for joining Sports Mole for tonight's match as Manchester United launch an incredible second-half comeback to beat Newcastle, who remain winless. I will leave you with our match report, and be sure to stick around for reaction too.
From me, though, it is goodbye for now.