Sir Alex Ferguson admitted Liverpool deserved to win the game at Anfield because United failed to cope with their physical approach.
In a subdued post-match interview, the United boss accepted the Reds were second best and was unhappy with the way his side conceded both goals in the 2-1 defeat.
“My overall view of the match is that Liverpool were the far better team,” the manager told MUTV.
“They tackled us, got about us and harassed us, forcing us to make mistakes, and we didn’t cope with that well. That was the source of our defeat.”
Carlos Tevez gave United a dream start when he converted debutant Dimitar Berbatov’s cross in the third minute, and for 20 minutes United’s recent stranglehold over the Merseysiders looked set to continue.
But Edwin van der Sar gifted Rafael Benitez's side an equaliser when he failed to deal with Xabi Alonso's deflected shot and the ball rebounded off Wes Brown into the net.
And substitute Ryan Babel delivered the killer blow in the second half after Ryan Giggs failed to deal with a ball on the by-line and was dispossessed by Dirk Kuyt.
“We started excellently with a wonderful ball from Berbatov to Tevez to put us in front, and at that point I thought we were going to establish
ourselves," continued Sir Alex.
“But the two goals we lost were absolute shockers; the defending was very, very poor. People will think they are watching a Conference side when they see the highlights.
“Apart from Rio Ferdinand, we did not have one good performance on the pitch. We were out-thought.”
Nemanja Vidic was sent off late on for a second bookable offence after a physical aerial challenge on Alonso and will miss next weekend’s tough trip to Chelsea.
“I’ve seen it and he led with his elbow,” Sir Alex admitted. “But [Jamie] Carragher and [Martin] Skrtel used their elbows in every aerial challenge in the game and there were no fouls given against them.
“We had three players booked and one sent off and I don’t think that’s a reflection of United being a dirty team.”
The Reds' boss will be demanding an immediate response as United look to end Chelsea’s long unbeaten record at Stamford Bridge next weekend.
“It’s going to be difficult but they are all difficult games away from home,” he added. “And if we don’t address the physical part of the game then we’ll struggle there too.”