iverpool recorded their biggest win at Old Trafford since 1936, coming from behind to win, with United having Nemanja Vidic sent off after the break for the second time this season against the Anfield side.Cristiano Ronaldo gave United the lead but Fernando Torres soon levelled and a Steven Gerrard penalty just before the break gave Liverpool the advantage before Fabio Aurelio and Andrea Dossena heaped further misery on the leaders."There is no complacency on our part," added Ferguson. "It was a bad day in terms of the goals we lost but I couldn't argue with the quality of play that much," he said."One or two players were a little bit short in terms of what we expect of them but I do know the football was good, we kept driving on and they showed good energy, even though we only had two-and-a-half days to prepare for the match."United legend Sir Bobby Charlton told BBC Radio 5 Live's Sportsweek that the defeat could even help strengthen the champions' resolve through the title run-in.