United never really challenged them offensively because Mourinho had no intention to do that.
As mentioned above they've lost 5-1 away against Eibar three weeks ago and before that also 5-3 at Pizjuan in Seville derby in January. They are missing defenders like Kjaer and Corchia but defense has been their weakness for years. They got away with Emery's more defensive tactics but now that they're playing more possesion oriented football under Montella and before Berizzo and Sampaoli, they are more exposed defensively. They've conceded 40 goals already this season, the same as last placed Malaga. Only Las Palmas, Deportivo, Sociedad and Betis have conceded more.