A typical United home performance this season, to give Celta Vigo their due they are not that bad a side. Their league position is in no small way due to them prioritising both the Europa League and the Spanish Cup. They knocked Real Madrid out of the Spanish Cup and earlier in the season beat Barca 4-3 at Camp Nou. They have been resting six or seven first choice players for months now, hence the lowly league position.
All in all a very sloppy display from United I will agree.