Manchester United have it all to do after falling to a 2-0 defeat against Paris Saint-Germain at Old Trafford, the first setback of Ole Gunnar Solskjaer's caretaker spell.
Goals from Presnel Kimpembe and Kylian Mbappé ensured the Parisians take a commanding lead back to the French capital, not to mention two valuable away goals.
Solskjaer's side are not out of the tie but have a huge task on their hands at the Parc des Princes, where PSG could have Edinson Cavani and Thomas Meunier back to full fitness.
If United are are to complete a memorable comeback, then they will have to do so without Paul Pogba.
Pogba, a Paris boy himself, will miss the return leg after receiving a second yellow card in the dying minutes of a disappointing and possibly season-defining defeat.
Five things we learned
Solskjaer’s revolution receives difficult reality check
After eight weeks, ten victories and much progress, Solskjaer has received a reality check. This was the first defeat of his caretaker spell and an especially chastening one, as it arrived in the very first meeting his United and a genuine European superpower.
It would be mean-spirited to suggest that this result had been coming or was in any way inevitable, given how optimistic many were about United's chances of securing a first-leg lead before kick-off. But after doing little but lift the mood around these parts of Manchester, Solskjaer perhaps now understands the scale of the task at hand.
If United are to return to their former glories, and if Solskjaer is to be the one tasked with their restoration, then this is the level that they must reach. Thomas Tuchel's visitors had more nous and know-how, edging a tightly-contested first half before dominating the second.
Given PSG's recent history in this competition, their two away goals do not kill this tie completely. Another remontada is not totally out of the question. But on this evidence, chances of United reaching their first Champions League quarter-final in eight years are slim.
Di Maria responds in best possible fashion
Team-mates of Angel di Maria felt he “could never hack” playing at Old Trafford during his days as a United player and, on this return to Manchester, his first-half display appeared to have proved them right.
United supporters are usually very accommodating towards their former players but Di Maria was booed upon his first touch of the ball, then jeered louder still when he duly ran the possession out of play. The biggest cheer of the first half came when Ashley Young clattered into him, bouncing Di Maria off the advertising boards.
It would have been easy, at that point, for Di Maria to wilt but Old Trafford witnessed a very different character from the feckless, fragile memory of him that has been cultivated in these parts.
His delivery for the corner from which Kimpembe scored was inch-perfect, confounding a defence which has frequently struggled with set pieces this season. And once he had a hand in putting his side a goal up, Di Maria could exact revenge on his tormentors in the crowd.
Those in Old Trafford's Scoreboard End bore the brunt of his frustration. It did not take an expert in lip-reading to understand what was said, nor just how much that moment meant to him.
Mbappé burns through United defence
Watching the world's most exciting young athlete brings to mind a quip by another who used to have a claim to that title. To paraphrase Mike Tyson: everyone has a plan until Kylian Mbappé puts his foot down.
The outstanding talent of last summer’s World Cup took half an hour or so to warm his engine up, but once ready, it took only one extraordinary burst of pace past Victor Lindelof to send a chill through Old Trafford.
The only real selection decision that Solskjaer had to make before kick-off came in the centre defence and he ultimately favoured Eric Bailly over Phil Jones, as the Ivorian’s superior speed would help better combat Mbappé.
It was little use. Without Edinson Cavani or Neymar’s runs to consider, Mbappé ghosted along United’s backline, picking and choosing his opponents as he pleased.
It just so happened that it was Bailly who failed to track him closely when he broke in behind, latched onto Di Maria's delicate pass to add the second.
United pay the price at set-pieces
It is perhaps the only area of United’s play which is yet to see considerable improvement under Solskjaer.
Jose Mourinho was unhappy with how his side defended set pieces during his doomed final months in charge and his replacement highlighted it as an area which needed work shortly after being appointed.
Yet when Di Maria delivered an excellent, swerving corner at the start the second half, a static United defence was found wanting. Nemanja Matic had made some key interceptions in the opening stages but let himself down at a crucial moment, losing the run of Kimpembe and allowing the centre-half to score.
United's defensive work in open play during the first half had been diligent and, in glimpses, impressive. It was suddenly undone in easily preventible fashion.
Loss of Lingard and Martial exposes lack of options
Though this was a disappointing defeat and a meagre response to going behind from United, Solskjaer may wonder what might have been had Jesse Lingard and Anthony Martial not received cruel injuries towards the end of the first half.
Lingard, in particular, had troubled PSG with his energy, movement and intricate passing. Though Martial was a more subdued presence, his speed on the break was a useful outlet which could no longer be called upon after the break.
Their replacements were Alexis Sanchez and Juan Mata. Sanchez, a shadow of his former Arsenal self, was utterly ineffective and Solskjaer could not hide from that fact in his post-match press conference.
Mata offers invention but little pace, which United so desperately needed to catch their visitors on the hoof. United's Plan A was therefore scuppered. Plan B never materialised.
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