#1 The kindness of the fixture list
It is a well established fact in football that home advantage counts for a lot in the game, as the passionate noise of roaring fans has been seen to give players an extra push to go all out for victory, and this is the reason why teams ensure to finish top of their respective groups in European competitions, to have the edge of playing the second leg of their knockout ties at home.
That being said, the fixture list is a bit kind to United, because most of their remaining away fixtures are against opponents who the Manchester giants are expected to win, while the matches against their main rivals would be played at home, with their only 'tough' fixture remaining being away to Arsenal at the Emirates.
Old Trafford was once a fortress feared by all, and even though we have come a long way from those glorious years, any team in the world would still be wise to accord the hallowed ground some respect upon visitation, and with their passionate fans behind them, United players could go all the way and finish in the top four.