Arsenal vs Manchester United: Five things we learned as Manchester United knock Arsenal out of the FA Cup

Arsenal mounted a valiant comeback in the second half, but were ultimately outwitted by Ole Gunnar Solskjaer

Manchester United knocked Arsenal out of the FA Cup with a 3-1 victory at the Emirates in their fourth-round tie.

After Arsenal’s quick start seemed to catch Ole Gunnar Solskjaer’s side off guard, United stunned the Gunners on the break as Romelu Lukaku‘s wonderful through-ball took out three defenders to set up a sublime finish by Alexis Sanchez at his old haunt.

Just three minutes later and that lead was two as an almost identical attack saw Lukaku act playmaker again, this time setting up Jesse Lingard, who passed the ball delicately into the bottom corner.

Arsenal bounced back on the stroke of half-time after a burst of cute skill saw Aaron Ramsey weave his way into the box and cut-back to Pierre-Emerick Aubameyang for the simplest of tap-ins.

Mesut Ozil made a rare appearance from the bench, tempers flared, Laurent Koscielny was brought off with a grim head injury, but after the various twists it was another well-crafted counter-attack, finished by Anthony Martial, that put United out of reach and into the fifth round.

Here are five things we learned...

The ghost of Alexis Sanchez returns at his old haunt

The Sanchez resuscitation bandwagon arrived at what seemed a landmark station tonight. Back on familiar turf, feeding off the Arsenal’s fans fury and breathing in the boos, this was the Chilean’s decisive chance to make himself a hero at Manchester United.

At first, it seemed as though it wouldn’t click. Backflicks ricocheted off ankles, cutbacks were cut off, duels with Maitland-Niles rarely brought profit. But then, in the 27th minute, the ghost of Sanchez past made his appearance. The Arsenal’s players couldn’t see Romelu Lukaku’s deft ball coming, but the 30-year-old did, dancing round Petr Cech and slotting into the top corner from a tight angle. Such was the pulse pouring through the forward, his eyes bulged as he celebrated. A vindication of chances missed, a start perhaps of something new at United, just as he was being written off.

Passmaster, playmaker, Romelu Lukaku gets creative

It was a pass few creative midfielders might have spotted. Lukaku galloped down the right-hand side into the space behind Sead Kolasinac. As he squared inside, three Arsenal defenders waited in a standoff, inviting the Belgian to shoot at goal from 20 yards.

But as Lukaku cocked his left leg, the Gunners defenders rushed forward blindly and, only then, with barely a look in their direction, did he flick a soft pass inside to Sanchez. Perfectly weighted and, thanks to Sanchez, perfectly finished. Three minutes later and Lukaku was at it again, flying down the wing again to tee-up Jesse Lingard, who added United’s second. So often has the Belgian been criticised for his lack of goals this season, a clumsy indecisivenesss when on the break. Here, Lukaku showed once again that he is capable of so much more.

Alexis Sanchez celebrates after scoring United’s first (AFP/Getty)

The Battle of Tactics: Ole 1 – Unai 0

Having spent half a season at the helm, Unai Emery should in theory have the better grasp of his side than Ole Gunnar Solskjaer. Yet, the Norwegian seems to have settled his team into a groove so well in such a short space of time.

The same counter-attacking tactics which outfoxed Tottenham at Wembley, undid Arsenal at the Emirates. Even when Arsenal made a fast start, United remained patient and predatory.

Coiled back, they invited Sead Kolasinac to bulldozer forward with Lukaku pincered to the touchline waiting to dash. The plot worked every time. For the first goal, by the time the Bosnian had turned around to realise the danger, Lukaku was ten metres beyond him en route to assisting the first goal.

Solskjaer isolated the weak point in Emery’s 4-4-2, and then United danced all over that creaky floorboard.

Aaron Ramsey runs Arsenal’s midfield again

Mesut Ozil never had a dusty sniff at a starting position after Ramsey’s standout performance against Chelsea last weekend. Ostensibly at No 10, the Welshman proved how, perhaps through necessity under Emery, he has shirked his ‘luxury player’ tag and become a force in midfield. Throughout the game, Ramsey orchestrated Arsenal’s attack, created pockets of space and interchanged freely with Lucas Torreira and Granit Xhaka. Despite supposedly in the central-attacking role, he drifted across to either flank, sunk back into more of a box-to-box type function, giving the Gunners a fluidity between attack and defence.

Ramsey was integral to every portion of Arsenal’s success this evening, and the summation of his recent improvement came in the goal; a blaze of stepovers – the type of flash skill he’s never seemed quite natural at – losing Bailly as he ran into the box before setting up Aubameyang for Arsenal’s goal.

For the second game in a row, the Welshman was Arsenal’s best player, and just as so often comes with that reputation, is an impending departure.

Maitland-Niles impressed replacing the injured Hector Bellerin (Getty)

Ainsley Maitland-Niles stands firm in his greatest test

You’re 21 years old, filling-in in an out of favour position, your biggest test and the chance to hold down a first-team place for the rest of the season after Hector Bellerin’s ACL injury last week. Two minutes into the match, served a hospital pass on the edge of your own box, you look up to see Paul Pogba charging you down, Sanchez is waiting on the touchline, Lukaku is blocking the route back towards goal.

This was a game where Maitland-Niles could have crumbled, but instead the starlet showed his mettle. After two nervous moments in the opening minutes, when he was cheaply dispossessed, the right-back settled into the rhythm of an assured senior play, steady in defence, calm playing out, and dangerous when charging forwards. If this was an audition for his first team position, he stood firm to the test.