The result meant that United have now officially made the worst start of any side in the Premier League era after 10 games - with one point, no wins and a minus-22 goal difference - with yet more speculation about the future of boss Paul Heckingbottom certain to continue in the coming days.
United are certainly in a difficult spot, with opinions torn amongst the fanbase on the best course of action to get out of it. Here are seven talking points from the Emirates drubbing...
1. Defeat turns up the pressure
The narrative going into this game amongst the national press was that Paul Heckingbottom needed a win to save his job. Far, far better sides have lost to this Arsenal side this season and United travelled south battered, bruised and low on bodies, so defeat was no surprise. But the manner and extent of it now perhaps gives Prince Abdullah a decision to make on the future of his manager, and by extension the future of his club. Does he sell Heckingbottom short, having relied on his manager to look after him during the turbulent times of last season throughout reports of administration and a transfer embargo, while steering them to promotion and maximising the value of his asset exponentially? Or does he stand by his man, with a much more palatable run of fixtures on the horizon? United's Premier League status will not be defined by clashes against the likes of Arsenal, Spurs or Man City, who they have already faced this season. It will be decided by results against those around them - and with United left short-handed for winnable early-season games against Everton and Nottingham Forest, the decent thing would surely be to give Heckingbottom the upcoming games against Wolves, Bournemouth and the likes...
2. No magic wand?
Whoever would come in to replace Heckingbottom, if he was dismissed, would have to weave some magic to get a better tune out of players who are clearly low on confidence and belief and struggling to establish themselves at this level. There would be no scope to change things in terms of new players until January - if there would be any budget anyway, with Prince Abdullah showing in the past he is not afraid to put away the chequebook if he believes relegation is already a virtual certainty - and with so many injuries, there wouldn't be even much wiggle room in terms of formation either. So with the same personnel, the same formation and the same devoid-of-belief mood, could anyone come in and wave a magic wand to change things instantly? No-one is happy with the situation at the minute but it cannot be change for change's sake when so much has been made of Heckingbottom's appointment and the long-term vision it heralded. United's hierarchy said at the time that he would not be judged on results and that approach will be tested more than ever right now.
3. More questions over Wes
Make no mistake, Wes Foderingham has been one of the leading lights of United's season so far and without a number of his excellent saves, their campaign would be looking even bleaker than it currently does. But that doesn't make him immune to criticism or question marks, either and although some of the stick he got for his handling of Diego Dalot's winner for Manchester United last week felt a little harsh, his work for the second of Eddie Nketiah's three goals at the Emirates won't be something he looks back on with much fondness. There was pressure from Ben White - enough to prompt a VAR check for a potential foul - but Foderingham didn't deal with the corner well enough and Nketiah gleefully accepted the invitation. With the sheer amount of work he has been tasked with this season, a drop-off in form was perhaps inevitable and Foderingham will hope for a somewhat easier afternoon next weekend when Wolves visit Bramall Lane
4. Heckingbottom's biggest disappointment
The Blades chief was unhappy with the manner of many of Arsenal's goals and also the way that his side lost the physical battle against the Gunners. The Blades were always going to be up against it in terms of football but had to compete physically to stand a chance of narrowing the gap, and they couldn't do that either. It was doable - up until Nketiah's opener before the half-hour mark, goalkeeper Foderingham didn't have a save to make and although Arsenal dominated possession, much of it was in front of them. Then the concession of a first goal Heckingbottom described as really poor - Declan Rice given far too much time to pick the cross, Auston Trusty making a rare misstep as Nketiah rounded him - put the writing on the wall in terms of the outcome, if not its margin. "Their aggression, the one-v-one moments, got them on top and that was the biggest difference," Heckingbottom said. "We'd gone from frustrating them in the first half to conceding the second goal really quickly in the second half. A tough place to come at 2-0 down and they stepped on the gas a little bit."