They say you can’t teach an old dog new tricks.

Arsène Wenger may prefer the idea of being a wily old fox, but when it came to making the right decisions at moments that mattered against United, the Arsenal manager came up trumps.

First up the selection – Danny Welbeck’s inclusion raised a few eyebrows, particularly given Olivier Giroud’s fantastic record in this competition, and certainly at half time the discussion was around when not if the Frenchman would replace his English teammate.

The former United man struggled to hold the ball up in the first half and took some dodgy touches in good positions when Arsenal did get bodies up around him. However, the manager stuck with him and following half time the difference was noticable.

Welbeck started making a real nuisance of himself, tracking back, giving United’s deeper midfielders no time and space, and also harrying defenders in the fashion that ultimately led to his goal.

A good selection.

Then the substitutions – when the Ox limped towards the touchline to be replaced thd crowd were baying for the introduction of Theo Walcott, but the manager opted or the solidity of Aaron Ramsey in the centre of the park and shifted the excellent Ozil into a wider role.

Not only was Walcott’s lightweight style unsuitable for the aggression of the game, but it also gave greater support for Coquelin and Cazorla in the central area, allowing the Frenchman to drop deeper to help out his centre backs with Fellaini by cutting off the front ball.

It also freed up Ozil to run the show from the right wing.

Then came something we’ve rarely seen from Wenger – a proactive substitution on a player walking a tightrope. Hector Bellerin got himself booked for a pretty rash challenge in the opening few minutes and had been continuing to go into committed tackles all game.

In the 64th minute, the Spanish teenager brought Ashley Young down (shortly after a shocking challenge on Cazorla by Rojo!) and the United man made the absolute most of it. Referee Oliver was unmoved but with a yellow card and a number of fouls to his name, Wenger made the call to hook his young fullback and replace him with Calum Chambers.

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It was a brave call to make in light of Chambers’ recent flaky form, and one very out of character from the Arsenal manager. It’s easy to forget Bellerin’s age and inexperience given the maturity of recent performances, but it was absolutely the right decision from the manager to take him out of the firing line.

Finally, the way we set up for the game was refreshing.

Perhaps it wasn’t the same level of surprise as our away performance at City, but with the way United are playing at the moment it would have been very easy to approach the game with a view that if we play our way, that’s all that matters.

We came out with a very solid base, with Oxlade-Chamberlain and Alexis really grafting in front of their fullbacks, Cazorla disciplined in sitting alongside Coquelin, and ensuring at least one fullback was always tucked in alongside the centre halves. Most refreshingly, Arsène sent his men out to attack in small but efficient groups, with rarely more than four players committed to any one attack.

Player ratings are all the rage these days (and you can read ours here!) but if the manager was being scored tonight he’d have been right at the top end of the spectrum.

One swallow does not a summer make, and he certainly has some frustrating habits (!) but if Arsène can influence games like he did tonight then we may yet have a very successful season.

We’re the famous Arsenal, and we’re going to Wembley!

@nellypop13