Phil Jones has admitted Manchester United "did not show up" at Newcastle and deserved to lose at St James' Park because they were "not good enough."
Matt Ritchie scored the only goal of the game in the second half and while United had chances, they could not find a way past debutant goalkeeper Martin Dubravka.
Jones told MUTV: "We didn't show up today, we started slowly and they pressed us and the crowd were on their feet.
"We got control midway through the first half and should have scored. We had a few chances cleared off the line, but we weren't at the races, we weren't good enough, it's as simple as that.
"Ultimately we have conceded a sloppy goal and the lads are devastated in the dressing room."
Dubravka, on loan from Sparta Prague, was by far the busier goalkeeper after saving from Anthony Martial and substitute Michael Carrick.
However, Jones, visibly frustrated in the second half after screaming at his midfielders to give the defence more protection, refused to put the result down to luck.
United will aim to bounce back when they face Huddersfield in the FA Cup fifth round at the John Smith's Stadium on Saturday.
Jones added: "In the last 10 or 15 minutes, we had three or four balls cleared off the line.
"They were scrapping for their lives and that is the sort of luck they needed and they got it.
"But it wasn't bad luck today, we just weren't good enough and I don't think we deserved to win the game.
"A lot of teams around us keep drawing and losing points so there is a lot still to play for. It was a disappointing day today, but we have to go again. That is all we can do and that is all we know. We have to improve."