Liverpool manager Jurgen Klopp sought out the positives after his side were dealt another crushing blow in their faltering season.
Liverpool showed glimpses of their attacking best, but could not contain a vibrant Man Utd attack.
Mohamed Salah notched twice, though a costly error from Rhys Williams and a poor foul from Fabinho handed their opponents the chances they required to advance to the fifth round.
Speaking to the BBC after the match, Klopp said: “There was a lot of good things and some mistakes around the goals. If you want to win here you have to be absolutely top and we were not.
“For the first goal we had no protection, we wanted it too much. Things like this should not happen but they can happen. We had too many players in a receiving position.
“We can take things out of this game, we try to learn from every game. It’s good for Mo Salah, good for the confidence.
“It was a tough game. We want it hard but tonight it was not enough.
“If you win a game there are negatives, if you lose a game too but I saw the boys really, really wanted it.
“We had problems on the counter-attack, it was intense, but there were positives.”