LONDON -- This could have been the game that saw Jose Mourinho rediscover his managerial mojo, but Paul Pogba's second-half red card ensures we might have to wait a little longer before learning whether the Special One really is ready to take on Pep Guardiola.
Before Manchester United's 3-1 victory at the Emirates, Mourinho's season-and-a-half at Old Trafford had been a tale of progress, but the kind that hit a brick wall whenever the opponent was a top-six outfit playing at home.
Seven previous away days against the Premier League's best had resulted in zero wins, one goal -- in a 2-1 defeat at Tottenham -- and a heap of negativity on the back of some unambitious, safety-first performances at Liverpool, Chelsea, Arsenal, Spurs and Manchester City.
But on Saturday, Mourinho sent United out on the front foot. It was a "fortune favours the brave" performance, with blistering counter-attacking play that blew Arsenal apart as the away side raced into a 2-0 lead after only 11 minutes.
There was no caution, no negativity, and although goalkeeper David De Gea ended up as man of the match, having made 14 saves, this was not one of those games in which Mourinho "parked the bus" with the intention of escaping with a point.
Instead, it was like the early days of his first spell at Chelsea more than a decade ago: Hit a big opponent early, soak up pressure and then hit them again. And it was all going so well until Pogba saw red on 74 minutes, rightly being sent off by referee Andre Marriner for plunging his studs into the thigh of Gunners right-back Hector Bellerin.
United had just taken a 3-1 lead after Pogba set up Jesse Lingard's second goal of the game, which checked Arsenal after Alexandre Lacazette halved the home side's deficit, and would hold on to claim the three points that move them to within five of Man City, who host West Ham on Sunday.
But Pogba's sending off means he will miss the pivotal derby clash against the leaders on Dec. 10, and more than likely force Mourinho back into his shell. With the French midfielder in his lineup ahead of the defensive safety net provided by Nemanja Matic, United's manager is more prepared to take teams on. But without Pogba, he lacks a player capable of breaking from box to box, and the game plan is compromised as a result.
United won games when he missed nine weeks through injury earlier this season, but lacked impetus during many of those fixtures. Pogba provides jet fuel when he plays; without him, United run on diesel. So the problem for Mourinho as he looks ahead to the biggest game of the season is how to fill the huge hole left by Pogba's moment of madness.
Quite simply, he does not have an obvious answer because nobody else in United's squad has similar qualities -- that's why you spend £89 million on one player -- and Mourinho may also still be without Marouane Fellaini and Michael Carrick on derby day, further stretching his midfield options.
Henrikh Mkhitaryan is an option to come back into the team, as is Juan Mata, but their creativity in the final third will not replace the energy and game-stretching qualities of Pogba. Lingard, meanwhile, whose recent performances have justified Mourinho's faith, can do the box-to-box role but he does not possess the same vision or physical presence.
The Pogba headache will be compounded by Romelu Lukaku's ongoing form slump. The Belgian forward was again poor at the Emirates and his recent run stands at just one goal in his past 12 games for United.
Indeed, had Zlatan Ibrahimovic been fit to travel to Arsenal, Lukaku may even have been dropped. He will surely be rested against CSKA Moscow on Tuesday, but on this form, can Mourinho start him in the derby?
Whatever is decided, do not expect as open a game as we saw on Saturday. No Pogba reduces United's chances of victory against Guardiola's rampant side and makes it likely that Mourinho will revert to a safety-first approach in an attempt to grind out a vital win.