MATTHIJS de Ligt and Marcus Rashford grabbed the first-half goals to postpone the next Erik ten Hag crisis for at least another week.
But Manchester United were let off the hook by a Southampton side who outplayed them in the opening half an hour and failed to convert a penalty.
It would have been fascinating to see how United responded to that kind of setback.
In the end, though, Ten Hag’s side ran out comfortable enough winners and he avoided becoming the first United boss to lose three Premier League games in a row since 2015.
The Saints never recovered from somehow finding themselves two down at the break after striker Cameron Archer let them down at both ends.
First the £15m summer signing hit his spotkick far too close to United goalkeeper Andre Onana after Diogo Dalot brought down teenage winger Tyler Dibling.
De Ligt headed United into the lead a few minutes later and then Archer was guilty of failing to close down Rashford, who curled a fine shot in off the far post to make it two.
The Saints’ misery was complete when captain Jack Stephens was shown a straight red card – somewhat harshly – for a cynical lunge on United substitute Alejandro Garnacho, who made it three in stoppage-time from Dalot’s cross.
It was a bitter end to a game that had started so well for the home team.
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Dibling, 18, one of four home players making their first Premier League start for the club, skinned Dalot as early as the seventh minute and forced a save out of Onana.
Joshua Zirkzee had a great chance at the other end when Eriksen touched the ball into his path but the Dutchman’s shot on the stretch from inside the six-yard box was not good enough to beat Aaron Ramsdale.
In the 17th minute, Kyle Walker-Peters made De Ligt look like a novice but failed to find the right pass from the byline. United broke down the other end and Bruno Fernandes shot well wide.
Southampton looked much the better team.
Dalot’s torment continued when Mateus Fernandes cut inside him and fired in a cross-shot that De Ligt cut out.
And when the United full back fouled Dibling, Lesley Ugochukwu sent a free header over the bar from Yuki Sugawara’s free kick.
But Dalot’s luck seemed to have run out when he was once more beaten by Dibling and brought him down in the box.
Ben Brereton Diaz has a good record from the penalty spot yet the Saints forward handed the ball to Archer.
The young striker’s spotkick was far too close to Onana who saved to his right and had plenty of time to stand up and save Archer’s headed follow-up.
Punishment was not long coming. Ramsdale saved a deflected shot by Zirkzee but his defence was sleeping from the resulting corner.
It was played short to Fernandes and De Ligt headed the fine cross out of reach of Ramsdale’s right arm.
A minutes later, Southampton were guilty of the same kind of failure.
Ramsdale made a good save from Rashford after another United break. This time the corner was overhit, but in the second pahse poor Archer failed to close down Rashford quick enough and his well-placed shot went in off the far post.
United started the second half on the front foot. Full back Noussair Mazraoui hit the outside of the post and Rashford had a shot blocked by Jan Bednarek.
Southampton did not look like a team who believed they could find a way back into the game.
United, and Amad Diallo in particular, sensed their fragility and only some last-ditch defending stopped the visitors extending their lead.
Then it was Ramsdale’s turn as he leapt athletically to push away a long-range shot by Rashford, whose confidence had risen visibly.
At that point, just after the hour, Martin made four substitutions. The decision to include Dibling in the players taken off was not popular with the home crowd.
Not much changed, or not enough, anyway.
Southampton did not create a single opening and their frustration told in the final 10 minutes.
As Garnacho tried to scamper down the left touchline, Stephens took him out. A yellow card looked like sufficient punishment, but Attwell reached for his red.
Garnacho’s late third underlined that those anticipating the dismissal of Ten Hag will have to wait.
