Marcus Rashford was the hero for United as he came off the bench to grab a late, late winner to ensure his team continued their one hundred percent start to the season.
Coming into the match both sides had started the season unbeaten which for former United assistant Mike Phelan's team is something of a surprise as he has only been able to call on thirteen available players from his first team squad.
Mourinho spent the week trimming his own squad with more fringe players departing on loan or in the case of Tyler Blackett on permanent deals. He indicated that with only a week to go in the transfer market he wouldn't be bringing in any new players and that he was happy with his current squad who he believed could not only challenge for the Premier League but indeed go on and win it.
The players he chose to start the clash with Hull were: De Gea, Valencia, Blind, Bailly, Shaw, Fellaini, Pogba, Mata, Rooney, Ibrahimovic and Martial.
So Mourinho was able to pick an unchanged side that defeated Southampton at Old Trafford last week, which meant that Mkhitaryan would have to wait a little longer for his first start of the season. Alongside him on the bench were Smalling, Herrera, Schneiderlin, Young and Rashford who was called up to the England U21's for the first time this week.
The Red Devil's kicked off against a Hull side who haven't beaten United for 42 years when both the teams were in the old second division.
It took Ibrahimovic only two minutes to attempt the spectacular as he connected with a superb cross from the impressive Valencia from the right wing.
The Swede then came ever so close with a towering header that only just crept over the crossbar. Martial did well to deliver the ball onto the head of Ibrahimovic.
In the opening fifteen minutes, United looked a tight unit with Fellaini sitting deeper in midfield to allow Pogba to venture forward. The pace was a little leisurely which suited the away side who seemed to be biding their time to strike.
The first booking of the match was awarded to Fellaini for a clumsy challenge from behind in a dangerous area. Having been booked the Belgian continued to protest his innocence and Rooney had to intervene to stop referee Moss from taking any further action under the new discipline guidelines.
Fellaini would have to tread more carefully during the remainder of the match on a ground where he was sent off the last time United played there.
Luke Shaw showed his defensive class as he did enough to put off Snodgrass from connecting with the ball at the far post. Brilliant defending from Shaw who fully deserves a recall to the England squad.
Once again the United away supporters were in great voice as the rain hurtled down.
Pogba came close with a snap shot that keeper Jakupovic did well to collect on the slippery surface.
It was United's turn to try their luck with a free-kick on the edge of Hull's penalty area after Mata had been brought down. It was Mata himself who got to his feet and took the kick which was far too easy for the keeper.
The big Swede was causing the home defence all sorts of problems with not only his height but his terrific awareness of where his teammates were at any given time and his first touch was sublime at times.
With all the height United have at their disposal it was a surprise to see Juan Mata leap the highest to flick on a cross by Valencia that almost beat the keeper.
United were awarded a free kick that Ibrahimovic managed to get on the end of and backheeled the ball into the side netting with an audacious piece of skill.
That was the last chance of the first half a half in which United had dominated but failed to capitalise on all the possession they had. Sounds a lot like last season the main difference being with Mourinho's side you feel that a goal is going to come.
Mata seemed to struggle with his game out on the right-hand side and it wouldn't be a big surprise if a change happens and Mkhitaryan is brought into that position to provide more penetration.
Hull were there for the taking if only United could use the width more and get behind the full backs. Their forward play was all too narrow and easy for the home side to defend against.
The second half got underway with Mourinho deciding against making any changes. The injury crises for Phelan and Hull got worse as Snodgrass had to be withdrawn within the first few minutes of the restart.
United captain Rooney had the first opportunity as his head met a smart cross from Shaw but it fell too nicely for the keeper.
Nothing was working for United as they resorted to long balls into the area aimed at the head of Ibrahimovic, who was continually surrounded by two or three defenders. Something clearly had to change if they were to come away with all the points.
Mourinho had seen enough and decided that Martial didn't have his game on and introduced Mkhitaryan on the hour mark.
United won a corner after Ibrahimovic had thrashed a shot goalward from the edge of the box. This was followed by a neat move involving Pogba, Ibrahimovic and Mata which resulted in a trip on Mata in the area and a big shout for a penalty but the flag had gone up for offside.
Frustrations were running high as was shown in the reaction of Ibrahimovic when Mata took the ball from his feet as he pulled back the trigger to shoot. Pogba then blasted an attempt from 30 yards that was well over the bar.
As the rain continued to pour down Mkhitaryan showed his pace as he sped towards goal only to be upended by Huddlestone who was rightly booked.
Before the free-kick could be taken United made another change by bringing on Rashford at the expense of Mata for the remaining twenty minutes. The resulting free kick was blasted into the wall by Ibrahimovic.
The away fans had a break from singing to shout for a penalty after the ball had struck a defender on the upper arm but the referee waved play on. It was a clear penalty, but with the inconsistency the Premier League refs are showing it was no surprise nothing was given. Handball is handball whichever way you look at it.
Hull came alive in a five-minute spell that woke up their own fans when a shot was deflected for a corner with De Gea completely wrong-footed. With their best spell in the match, they didn't even manage to force a save from De Gea.
French star Pogba was the latest to try his luck from a free-kick again awarded to United on the edge of the area but he curled his effort well wide.
As the match entered the last ten minutes it was all United as Rashford showed what he can do with a run followed by a piercing drive that was brilliantly saved by the keeper.
Then Rashford and Ibrahimovic cleverly worked the ball through a group of players to pick out Mkhitaryan whose first-time effort was blocked. The tempo had been raised and the points were there for the taking as United won a string of corners.
An exceptional cross by the lively Rashford right across the six-yard box only had to be tapped in by one of his teammates, but they were slow to react and the chance had gone.
Rashford enjoyed an excellent cameo since his introduction and along with fellow substitute Mkhitaryan changed the style of United's play with such great effect.
A curling chance by Pogba almost found its way into the net but was only a whisker wide. Mourinho shouted his displeasure from the touchline when yet another Pogba effort found the back of the stand and not the back of the net.
Then just when you thought United would have to settle for a point Rashford stepped up and smashed the ball into the net from close range to give his side a valuable win and the precious three points in the 92nd minute.
It all came from great wing play by Rooney, who did extremely well on the left when he cut into the box and delivered a delightful ball on a plate for Rashford who finished with aplomb. It was to be Rooney's last action as he was substituted for Smalling.
The match had changed once the vibrant Rashford was introduced as his all round play had a positive impact on the way United attacked as he was causing damage on the left and the right and the Hull defenders struggled to cope with his constant surges into their area. With Martial slightly of the boil this could be the youngsters chance to grab a starting place.
It will be said that he had a point to prove after not being chosen in the opening games and Allardyce's first England squad, but that is just not true as when you have the talent this lad has there is absolutely nothing to prove.
For the third time in the new season, Eric Bailly picked up the Man of the Match award for another solid display alongside Daley Blind in the centre of defence. However, for the impact he had on the match since his introduction Rashford has also to be considered.
There will be many more tests like this one during the season and it was pleasing that the team never gave up the chase and finally managed to break down a resolute defence. It is still a work in progress, but if they can keep collecting maximum points while ironing out the kinks then we can all live with that.
There were two cup competitions drawn this week. In the first United were picked to play away at Northampton in the Football League Cup 3rd round add to that the draw for the Europa League took place and United were handed a mixed bag of games including a trip to Istanbul to face Fenerbahce, which is never easy, a closer to home trip to Holland against Feyenoord and a long journey to the Ukraine to play the relatively unknown FC Zorya Luhansk.
One interesting aspect of the draw will be the return of former United striker and fans favourite Robin van Persie who has in fact played for both United and Feyenoord and is currently at Fenerbahce.
There will be a break in the league action next weekend so next up for United is the mouth-watering derby and the first meeting of Jose and Pep as Manchester managers.
Until then thanks for reading.
Miles Dunton.