#2 Home advantage
Playing at Old Trafford is rarely easy for visiting teams. This is largely due to the history and standard set by Sir Alex Ferguson. He made Old Trafford a fortress, and that mentality has stuck till date.
United will line up against Palace with the full voice of their fans behind them. This is particularly important when it comes to motivating the players and giving them that extra dose of urgency in their play.
Despite the team's dismal first quarter of the campaign, the fans have stuck by the team and that will be pivotal in getting them out of their slump.
It is always an advantage to play at your home ground because the players are familiar with the pitch. What United need to do is seal those loopholes in defense and feed off the fans' energy in order to defeat Palace.