Let's think about everything that Arsenal did to defeat Tottenham Hotspur last week. Whether the factors that caused the result were repeatable or complete anomalies, we need consider them for a minute. This is not a piece about that game, but a large volume of the things that happened last week are relevant to this week.
Here's a short list of things that Arsenal did/has that caused them to win at the Emirates on Sunday:
Robin van Persie is a world class player
Scott Parker had a bad game
Theo Walcott had his best game in four years
Tomas Rosicky had his best game in god knows how long
They had a numerical advantage in the middle
Our fullbacks were caught up the pitch and burned by a fast wide player
We played slow central defenders too high up the pitch
Rosicky was given too much space and time on the ball
How many of those things, if repeated, could apply to the Manchester United game? Unfortunately, the vast majority of them. United are a team with better wingers than Arsenal, and Wayne Rooney is worlds better than Rosicky. Though Javier Hernandez and Danny Welbeck aren't nearly as good as van Persie, both are very fast and are excellent finishers. They torch teams who play high lines. United will play two central midfielders and Rooney, who comes deep enough, works hard enough and defends well enough to make it a virtual midfield three. Sandro, while wildly talented, does not have the experience and composure of Scott Parker and is certainly more likely to lose his cool in a big moment. Almost every advantage that Arsenal had on Tottenham could potentially apply to this game.
That's not to say that we should consider Tottenham as massive underdogs, or that Manchester United will win for sure if they play well. Tottenham's players could have been negatively affected by playing an away match in a derby. Arsenal's players could have been positively affected by playing at home in a derby. I am not a professional athlete and I do not know any of the Tottenham players personally, so I can't speak to how big of an affect these things have on players. But when very out of form players like Rosicky and Walcott have spectacular games while a very in form player like Parker plays an abysmal game, it's a reasonable conclusion to draw.
Tottenham will probably play better than they did last week in this game. United will probably be slightly less motivated than Arsenal were. This doesn't change the fact that, if Harry Redknapp doesn't make some serious alterations to his team and his normal strategy, there are serious matchup nightmares on the pitch for Spurs.
The biggest of these is Wayne Rooney, who will return to the starting XI from illness. Since United's loss to FC Basel -- save for the poor performance at St. James' Park -- Rooney has been in absolutely stunning form. His work rate, off the ball movement, first touch, through balls and finishing are all considerably better than Rosicky. He will be playing the same position, as an attacking midfielder in front of two central midfielders and behind a striker. I'm going to have a lengthy post on just the issues he creates later on.
Hernandez and Welbeck are equally pacy, and they're equally composed finishers. Unlike van Persie, neither of them drops deep to find the ball very often, and both will simply sit on the back shoulder of the last defender and look for opportunities to run in behind. Welbeck is also very dangerous when he's deployed as a left winger cutting in on his right and looking to shoot, and the way he plays makes him look like an inverted version of Daniel Sturridge.
Nani will start on the right, and he's basically better than Theo Walcott at everything but running in a straight line. He's almost as fast, he's a better dribbler, he's a better crosser and he's a better finisher. Even for all of his dumb/selfish decisions, he still makes better decisions than Walcott on a regular basis. If Benoit Assou-Ekotto gets caught up the pitch, he's going to get torched. By someone who actually has two feet. And who can cross.
Had enough doom and gloom? There is some good news in all of this. Sandro and Jake Livermore are both athletic and talented enough to possibly contain Rooney. They may not have the experience and composure to do it consistently, but both have the raw talent. Paul Scholes is brilliant, but he's a little less versatile than Mikel Arteta at this point in his career. Michael Carrick's positioning is better than Alex Song, but he isn't half the athlete. Whoever United plays at right back isn't going to play the position as intelligently as Bacary Sagna. Luka Modric is spectacular, and will be better in this game than he was against Arsenal. He's too good to be poor two games in a row.
There are ways to counter what United does, but most of them center around countering Rooney specifically. That is its own post.