Manchester United 1-2 Arsenal: 5 talking points

Danny Welbeck scored on his return to Old Trafford to seal Arsenal's progression into the semi-finals of the FA Cup. The Gunners beat 10-man Manchester United, who played, the final 15 minutes without Angel Di Maria, who was booked twice in the space of a minute.The Gunners took the lead in the first half thanks to Nacho Monreal's composed finish, but United got back immediately through Wayne Rooney's immaculate header. Just when it looked as though the game was going to finish in a stale mate, Welbeck capitalised on Antonio Valencia's slack back pass to score against his former club and send Arsenal through to the semis where they will face either Bradford or Reading.Here are the major talking points from the game:

#1 Michael Oliver\'s refereeing master class

Refereeing is a difficult profession on its own. After all, who would want strangers analysing in detail, how they did their job. It is sometimes made even more difficult by the atmosphere in certain grounds. Old Trafford is a difficult ground to referee in, in the best of times, but when you have more than 60,000 supporters screaming into your ear, criticising every decision you make, it can't be easy.

But, Michael Oliver showed that if you have the courage and single-mindedness to do your job and not bother about what others say, you can certainly succeed. On Monday, Oliver showed just why he is one of the best referees in England, whether it was penalizing players for simulation, letting the game flow or understanding the nature of certain tackles and the state of the game. While his decisions may not have been popular with the home fans, they were certainly right and that is what the referees are supposed to do.

#2 Arsenal show plenty of grit and determination

In the ever-changing modern world, there are some things that have remained constant throughout. The sun rising on the east, fans moaning about referees while the players have a shocking game and Arsenal performing poorly in the big games. Even with their good run of form, a trip to Old Trafford was always going to be a daunting proposition especially considering they had lost nine of their last 10 games there, including an 8-2 hammering just a few seasons ago.

But, buoyed by the confidence of their previous trip to Manchester, when they beat City 2-0, the Gunners came knowing that they could do it in the tricky away games. And although it wasn't their finest performance and their defending, especially in the first half was disappointing, they won and are now through to the semi-finals of the FA Cup to play either Bradford or Reading. And after a string of disappointing away days in the big games, the result is all that will matter for Arsene Wenger.

#3 Di Maria\'s stupidity costs United

Sometimes all it takes is a little bit of common sense. Over the past few weeks, many have got on the back of Angel Di Maria and understandably so. The Argentine has been poor and all players, no matter how much they cost, deserve to be criticised when they don't deliver. But against Arsenal, he showed why United broke the bank to sign him, pace, penetration and precision in the final third with his assist for Wayne Rooney’s equalizer being the highlight till his mind went blank for a moment in the second half.

Having just been booked for diving, the best thing to do is to walk away from the scene. Instead, the 26-year-old stupidly decided to tug back at the referee's shirt and was rightly sent off. While poor performances can be forgiven and attributed to a lack of confidence, incidents like that smack of lack of common sense.

#4 Valencia is not a right back

While all the outcry in the build up to the season was the need for a centre back, many had conveniently forgotten the club's predicament in the right back area. Rafael's proneness to injury has meant that Antonio Valencia has almost been converted into a right back this season. And on Monday, Alexis Sanchez showed just why you need defenders doing the defensive work.

The Ecuadorian winger was at fault for both goals. He was out of position for the first and had a suicidal back pass intercepted for the second. Whilst his threat going forward was evident in this game as well, in the big games, you need defenders who can defend and Valencia certainly isn't a defender.

#5 Old Trafford is buzzing again

Sometimes even in defeat, there are clear positives you can take from the game. One such was the atmosphere at Old Trafford. There have been times when Old Trafford, the biggest club ground in England has seemed like a Sunday league crowd due to the lack of noise. Even the last home game against Sunderland was one that saw chants that only became apparent once United scored. At times, the crowd have been impatient and rightly so and chants of "attack, attack" are a new low in terms of the atmosphere in the grounds.

But, on Monday night, there was no question about the allegiance of home crowd, who sang, applauded, whistled and booed every effort from the first minute to the last. Van Gaal can blame plenty of things on the defeat to Arsenal, but lack of support from the crowd isn't one of them as the partisan crowd certainly played their part in making it an enthralling encounter.