#1 Lack of a proper No. 9

Another game without Romelu Lukaku and another game that proves the underlying difference he makes when he plays.
Mourinho's decision to field a team without a proper striker back-fired and as mentioned earlier, both Lingard and Sanchez looked to drop deep instead of running behind the defenders and stretching them.
This lack of running off the ball and into the box was rarely executed and as a result, their midfield trio often had to stay glued to their formation and thus negated the influence Pogba makes with his marauding runs into the box.
This forced them to play at such narrow spaces and operate very tightly. West Ham players easily outnumbered their counterparts in this aspect and despite the visitors having 16 shots on goal, all of them either went off target or were easy enough for Adrian to deal with.
Mourinho will want Lukaku fit for the FA Cup final at any cost after witnessing this display from the players he fielded tonight.