Alan O’Brien  Follow @alanob2112

Arsenal’s vulnerability to pressing is not a new development. Way back in August, Leicester City and Liverpool combined to hit seven past the Gunners by forcing final-third turnovers. The question is: why haven’t more clubs followed their lead?

Pressing

Tottenham Hotspur manager Mauricio Pochettino stands out as a particular culprit. A fortnight ago, the Argentinian let Arsenal’s shaky centre-backs off the hook with a conservative 3-5-1-1 system. Arsene Wenger confounded expectations by employing the very high-pressing game ‘Poch’ repopularised — to devastating effect.

José Mourinho, winless in eight trips to Big Six sides, was not about to err in the same manner. The same 3-4-1-2 formation that bested Watford in midweek worked a treat. Manchester United’s attacking triumvirate could confront Arsenal’s central-defensive trio man-for-man. And they did; sporadically, mind you, but they did. Jesse Lingard’s boundless energy again proved a particular boon in that regard.

Well-timed darts of pressure forced calamitous defensive-third errors from Laurent Koscielny and Skhodhran Mustafi. Incredibly, having drawn a blank in seven of those eight Big Six road-trips, Mourinho found his side two up inside 11 minutes.

Reorganisation

Mustafi’s injury afforded Wenger the chance to respond with a 4-2-3-1; the same change he felt compelled to make so frequently throughout those wretched opening weeks.

Mourinho, ever the in-game manager par excellence, predictably reacted immediately. But the results of his tweaking were anything but foreseeable. Captain Antonio Valencia was entrusted with the entire right-side, in a weirdly lop-sided 5-1-3-1 formation. Anthony Martial was pulled back from the front-line to mind Hector Bellerin. Nemanja Matic sat on number-10 Mesut Ozil, just behind Lingard and Paul Pogba.

United have undoubtedly benefited from Pogba’s flair since the Frenchman’s return from injury. But the midfielder’s indiscipline is becoming very hard to ignore.

Pogba

Recent league games against Newcastle United and Watford have seen United flounder in the face of midfield runners. Isaac Hayden ran off Pogba to miss a sitter for Rafa Benitez’s side. And neither Pogba nor Ander Herrera were visible when Abdoulaye Doucouré popped up to halve United’s lead in midweek.

Indeed, Mourinho felt compelled to comment on this obvious lack of “balance” in the wake of both fixtures. Reacting to Watford’s late comeback, the Portuguese remarked: “We needed to go back to our defensive stability, which we lost when Matic had to come out (injured).” Quite.

And boy was the Serbian in prime firefighting mode here. In the absence of sufficient assistance from his teammates, Matic engaged in an heroic blocking, tackling and intercepting solo mission; crucially denying Aaron Ramsey’s close-range effort on the half-hour mark. Only the wonderful David de Gea proved a better stopper.

Even a 23rd-minute touchline chat with the boss failed to get Pogba to restrain his positioning. It was therefore no surprise when Ramsey ran off his back to tee up Alexandre Lacazette’s goal.

Compactness

The Welsh midfielder ran onto Alexis Sanchez’s lofted penalty-area pass, a rare positive intervention from the Chilean here. Victor Lindelof again looked good in a back-three, using his mobility to get tight to Sanchez in much the same manner as Richarlison was shackled in midweek. The Swede’s weakness — namely some physically inadequate penalty-box defending — are masked in this system.

Although in retreat mode for much of the second-half, United attempted manfully to maintain their compactness. Lacazatte’s goal resulted from a failed attempt to play offside, as did the passage-of-play that forced de Gea to deny Sanchez and Lacazette in quick succession. Ashley Young, still a defensive work-in-progress, failed to stay in line with his team-mates.

But there was method to Mourinho’s apparent compactness madness, allowing United to connect more easily with a black shirt on the break. Lingard should have completed one such counter-attack in the 52nd minute, but made no mistake in the 63rd. The high-block is not the only long-held Arsenal vulnerability after all. For Pogba, read Ramsey, as the Gunners’ appalling defensive transitions let them down again.

Reorganisation (again)

Then Pogba’s indiscipline came back to bite again, as United were deservedly reduced to ten men. The midfielder will now miss next week’s derby clash with the ‘noisy neighbours’. Counter-intuitively, for all his talents, United may be better off without the former Juventus man against the channel-running of Kevin de Bruyne and David Silva.

Pogba’s dismissal forced Mourinho to abandon the counter-attack-minded introduction of Marcus Rashford. The Portuguese was surely hoping to punish Wenger’s gung-ho removal of so-called holding-midfielder Granit Xhaka. Matteo Darmian instead appeared at left-back in a 5-3-1, however, with Young shifted into central-midfield.

Mourinho need not have worried. Wenger’s concurrent change — his last one — completely banjaxed his side’s attacking play, helping United kill the contest.

Admittedly, the Gunners should have been granted at least one penalty-kick, for Darmian’s intervention on Danny Welbeck. But the sheer weight of numbers that prompted this was all Wenger’s late plan had going for it.

Conclusion

Bringing on Olivier Giroud, while setting up in a manner that denies the striker the wide service he craves makes no sense. Alex Iwobi’s stint at left-wing-back was never going to provide crosses for Arsenal’s four strikers. Meanwhile, instructing Bellerin to form a quasi-back-three with Koscielny and Nacho Monreal denied natural width on the other side too.

Then, Arsenal do sit 20th in the Premier League crosses-per-game standings, as Wenger has long considered targeting ‘the mixer’ an antiquated, wasteful, pursuit. In the end, wasteful about sums up his profilgate side, who translated an expected-goals tally of 4.55 into just one on the scoreboard — where it matters.

Follow the author, Alan O’Brien, on Twitter:  Follow @alanob2112