I just loved seeing Danny Welbeck celebrate his goal. It is a load of tosh when a former player doesn’t celebrate against his old team. Goalscoring is why we play/watch/support — and it’s a while since Danny scored one! United didn’t want to keep him, he left for Arsenal and here he was back at Old Trafford scoring a predatory winner. Danny Welbeck rounded David De Gea to score Arsenal's winner against Manchester United . Welbeck latched on to an weak pass from Antonio Valencia to take the ball past De Gea and score . Welbeck (left) celebrated his goal at Old Trafford despite the fact he used to play for United . Of course he should enjoy it. Before his goal, watching Danny for an hour was awkward TV. The ball was bouncing away from him. He looked desperate at times. Even when he went down in the box, I thought he could have gone on to get a shot away. How much did he want to get into that position to shoot? If you look at Chelsea striker Diego Costa, he just lives for the chances, but as soon as the ball drops for Danny, it’s as if you can hear his pulse racing through the TV and nerves get the better of him. There are lots of things you can work on in football, but goalscorers have that ice in their veins, like Robbie Fowler, Alan Shearer or Thierry Henry. It was staggering that Louis van Gaal did not turn to Radamel Falcao. The poor lad must be thinking: What am I doing here? Louis van Gaal did not use striker Falcao to rescue the game against Arsenal at Old Trafford . Michael Carrick (right) was brought on at half-time but Colombia forward Falcao was unused . I know he is not the player Manchester United thought they were getting, but isn’t it down to the manager to get the best out of him? Goalscorers change games but instead they chased the match with Daley Blind and Michael Carrick, two sitting midfielders, on the pitch. The defending from United for Arsenal’s first goal was unbelievable! Yes, it was a fantastic goal for Arsenal but the defending from United was scandalous.That’s not about tactics, that’s players needing to tackle. Three United players failed to stop Alex Oxlade-Chamberlain as he ran at them and Antonio Valencia – who was playing at right back – turned his back on the Arsenal player. Nacho Monreal wheels away to celebrate scoring Arsenal's first goal against United at Old Trafford . Alex Oxlade-Chamberlain breezed through the United defence to provide an assist for the Monreal goal . You cannot do that. Roy Keane was in the studio but he must have been thinking he should be putting his boots back on. Even Roy, at 43,would have put up more resistance. Oxlade-Chamberlain does very well, driving forward and creating the opening (it was nice skill from Mesut Ozil in the build up too), but they cannot be allowed to do that. This fixture used to have Keane v Vieira, but these two midfields were packed with different players and nobody more bold than Santi Cazorla. Santi Cazorla (second right) was in inspirational form as Arsenal secured a place in the FA Cup semi-final . He doesn’t crash into tackles, but he has a different type of courage; courage on the ball. He’ll take it in tight areas, uses both feet and always likes to get the play moving. I could watch him all day. Arsenal were shot to pieces in the 3-1 defeat by Monaco and if it had been down to me, Per Mertesacker would never have played for them again after his display that night. But his performance at Old Trafford showed character and a welcome return to form. Per Mertesacker (left) and Francis Coquelin (right) were particularly impressive for Arsenal at Old Trafford . Francis Coquelin is another who stood out here. Luke Shaw will come through this, but he is playing like he has the handbrake on. Is he being overcoached? What has happened to the marauding full back who played with such freedom for Southampton? He is only 19 and he will come again, but the player Manchester United signed for £30million would hit crosses on the run and did his best work at the top end of the pitch. He isn’t doing that now. It looks to me as if he’s thinking too much and that will be down to him trying to carry out instructions. Luke Shaw didn't enjoy his best night for United and has struggled to recapture his Southampton form . Marouane Fellaini's tireless work for United made him one of their standout players against Arsenal . He is going to be a star, but when you consider how Nathaniel Clyne is developing, why isn’t Shaw doing the same? He is a young man, who has had his injuries, but he is struggling and was taken off at half-time in a reshuffle that ultimately didn’t pay off. It is strange watching United and when their best player is Marouane Fellaini then it shows where they are. I’m not a Fellaini fan, but he is working hard and looks the player most likely to get them out of this hole. The irony is that he is a signing made by David Moyes .
Danny Welbeck struck Arsenal's FA Cup winner against Manchester United . He celebrated the goal and received a mixed reception when substituted . Maroune Fellaini was United's best player but Luke Shaw struggled . Man Utd and Arsenal SPECIAL: Are fans right to question Louis van Gaal? READ: Twitter reacts to Manchester United's FA Cup exit .