As he clambered to his feet to leave the press conference room, Jose Mourinho came up with a spontaneous joke which amused him so much that he repeated it twice more before actually leaving the room. “So, finally I lost against Arsenal!”

But Mourinho doesn’t go in for humour when he feels the desolation of defeat. He wore the demeanour of a contended man because there was substantially enough in this performance to suggest that the horrors of September – when his players were overwhelmed by Manchester City for 45 minutes and embarrassed at Watford – are over and that there is some equilibrium. These are febrile and uncertain times at Old Trafford and if someone on Saturday morning had offered Mourinho a 1-1 draw in which Arsenal’s only effort on target was their late equalising goal, then he would have certainly have taken it.

The defence was – and certainly is – the problem, even though Manchester United were depleted by injury. The central pairing was makeshift to its bootstraps, with Phil Jones, who has played three games all calendar year, and Marcos Rojo, of whom Mourinho memorably declared after the match: “No-one knows what he is.”

But with Luke Shaw frozen out of this squad and Chris Smalling in a state of even chillier relations with the manager, judging by Friday’s press conference, there will be more goals like the Arsenal equaliser. Alex Oxlade-Chamberlain’s run down the right was unchecked by Marcus Rashford and Olivier Giroud’s resulting header unchallenged by Jones. “We don’t have very strong people in the air to cope with the cross,” Mourinho admitted. He didn’t bother pointing out that there'd been an infringement on Jones, who was half way to the ground after a nudge by Laurent Koscielny when Giroud leapt.

Sparks did not fly between Wenger and Mourinho on the touchline (Getty)

This feels like a component part of United which will need attention in the January transfer window and certainly next summer. United have lacked a commanding central defender since Nemanja Vidic left, when Sir Alex Ferguson took his leave. Goals will be leaked. Mouriunho’s United trajectory is unlikely to be linear.

But though they have won only two in nine games in the Premier League, there are certainly consolations here. Overall, the afternoon was an emphatic demonstration of Mancunian superiority, with a goal which summed up all that had been the best in the team: a thrust down the right flank which was United’s main route of entry and a first-time, left-footed finish of supreme technical skill by Juan Mata, who’d been outstanding all afternoon.

Manchester United vs Arsenal player ratings Show all 22 1 /22 Manchester United vs Arsenal player ratings Manchester United vs Arsenal player ratings David de Gea - 5 A very uncharacteristic error for Mustafi’s opener, bizarrely befuddled by the bounce of the downward header. Somewhat atoned with some typically solid saves in the second half. AFP/Getty Images Manchester United vs Arsenal player ratings Eric Bailly - 6 A welcome returnee who stood up strongly at times. Could perhaps have shepherded youthful cohort Dalot outside him slightly better. Action Images via Reuters Manchester United vs Arsenal player ratings Chris Smalling - 6 Solid in the middle of the defensive three. Getty Images Manchester United vs Arsenal player ratings Marcos Rojo - 5 Regardless of whether it is his own goal or marked as Lacazette’s, a very poor error to allow the Frenchman the chance. REUTERS Manchester United vs Arsenal player ratings Diogo Dalot - 5 Very little impact on the game. One particularly lacklustre moment getting forward from right back but looking lost with so much time, wasting a chance to cross. Sead Kolasinac had some joy down Dalot’s channel. Getty Images Manchester United vs Arsenal player ratings Ander Herrera - 6 Showed alertness to retrieve and cut back for Martial to score, though could have been flagged offside. Combative otherwise. Action Images via Reuters Manchester United vs Arsenal player ratings Nemanja Matic - 7 Broke up play well and set the tone for Manchester United’s performance. A good showing. AFP/Getty Images Manchester United vs Arsenal player ratings Matteo Darmian - 6 Little of note either way. He and Bellerin seemed to cancel each other out, rather. EPA Manchester United vs Arsenal player ratings Jesse Lingard - 6 Took his goal nicely. Quiet elsewhere on a scrappy night. AFP/Getty Images Manchester United vs Arsenal player ratings Anthony Martial - 7 A birthday goal after following up a free kick well, before trudging off injured just after the hour mark. EPA Manchester United vs Arsenal player ratings Marcus Rashford - 6 Hit his free kick nicely to force Leno into the initial save EPA Manchester United vs Arsenal player ratings Bernd Leno - 5 Leno could perhaps have done better with Rashford’s free kick in the lead up to Martial’s leveller, and didn’t cover himself in glory for Lingard’s either. Getty Images Manchester United vs Arsenal player ratings Shkodran Mustafi - 6 A decent header down into the ground for his goal, though a huge helping hand from David De Gea. PA Manchester United vs Arsenal player ratings Sokratis Papastathopoulos - 6 Stout defensively for much of the 90 minutes. EPA Manchester United vs Arsenal player ratings Rob Holding - 5 Stretchered off after 36 minutes with a serious looking injury. Having found some form, a real shame for Arsenal. REUTERS Manchester United vs Arsenal player ratings Hector Bellerin - 6 As mentioned in Darmian’s rating, rather cancelled out. One sliced effort from the edge of the box. AFP/Getty Images Manchester United vs Arsenal player ratings Lucas Torreira - 6 Another spiky performance in midfield. He’s certainly added some much-needed bite, but ought to be careful not to go too far with his destructive duties. AFP Manchester United vs Arsenal player ratings Matteo Guendouzi - 6 Put himself about with energy and physicality. Not as accomplished a performance as we have seen from the young Frenchman, though not overawed by the big occasion by any means. Action Images via Reuters Manchester United vs Arsenal player ratings Lead Kolasinac - 5 An error to allow Lingard to equalise, and consistently wasteful despite often being the extra man over down Arsenal’s left. AP Manchester United vs Arsenal player ratings Aaron Ramsey - 6 Substituted at half time despite bravely trying to continue in real discomfort at the end of the first half. PA Manchester United vs Arsenal player ratings Alex Iwobi - 5 Missing the cutting edge. Plenty of graft, little to show for it. PA Manchester United vs Arsenal player ratings Pierre-Emerick Aubameyang - 6 Aubameyang will rue missing a good chance from close range in the second half flurry of action. AFP/Getty Images

Mata’s emergence as a player of attacking and creative menace in Mourinho’s United is one of the many unexpected aspects of these past three months, and testament to the maturity of the Spaniard, who had reason to fear the arrival of a manager who sold him to Old Trafford in the first place. He took a monumental ovation when leaving five minutes from time and a warm embrace from Mourinho.

The strength Paul Pogba displayed in setting the match-winning move in train, supplying a ball which Ander Herrara cut back for Mata, carried a significance too. Pogba did not propel the United engine but did enough in moments to suggest that he is developing into what United paid £89m for. Antonio Valencia was the surprise component, though, and at the hub of much that United offered in the first half.

Mata broke the deadlock mid-way through the second half (Getty)

Few of the Arsenal performances will live in the memory. Alexis Sanchez's was the best from them, spinning off Valencia beautifully on one first half occasion, advancing towards goal and drawing a foul, but Mesut Ozil added little to a promising early attacking thrust and Theo Walcott exerted barely any influence whatsoever. “Maybe it’s a mental block here because for a while it didn’t go well for us,” Wenger said later, which was highly unconvincing as assessments of aspiring champions go.

He looked extremely relieved as he made his own appearance in the press room, happily declaring it would be “pretentious” to claim that the equaliser – created and scored by substitutes was planned. United were actually architects of their own fate, by lacking ruthlessness. Rojo’s headed miss from a Daley Blind cross in the game’s closing stages was fairly criminal. It required two excellent saves from Petr Cech to divert a Mata shot and arced Anthony Martial effort wide of the same right upright.

Giroud rises to equalise late on, beating Jones in the air (Getty)

It was Valencia, in a surprise first start since breaking an arm against Manchester City in the EFL Cup last month, who created the game’s moment of controversy, rolling around the outside of Nacho Monreal in the 35th minuteand going down as the Spaniard reached across him. There were grounds for a penalty - Monreal had his arm on Valencia – but the player just went to earth too easily and Andre Marriner’s decision not to penalise was fair.

Mourinho’s reflections on all of this included a long list of why other teams have it easier than United, including the time “Maurice” Pochettino has had to assemble a Spurs side. (After Mourinho's talk of “Gary” Southgate on Friday, this is becoming a comedy sideshow.) When you're on the defensive, a convincing performance against Arsenal is triumph, whatever the final score.

Manchester United (4-2-3-1): De Gea; Valencia, Rojo, Jones, Darmian (Blind 64) ; Carrick, Herrera; Mata (Schneiderlin 85), Pogba, Martial (Rooney 53); Rashford.

Substitutes: Romero, Memphis, Rooney, Blind, Young.

Arsenal (4-2-3-1): Cech; Jenkinson (Oxlade-Chamberlain 84), Mustafi, Koscielny, Monreal; Coquelin (Xhaka 80), Ramsey; Walcott, Ozil, Mustafi; Sanchez.

Substitutes: Ospina, Gibbs, Paulista, Giroud, Iwobi.