It has, however, dented Sir Alex Ferguson's side's hopes of a straightforward run-in and at the same time restored some pride for the Reds after two defeats at Old Trafford already this campaign.
Dirk Kuyt grabbed the headlines with a first Liverpool hat-trick against United since Peter Beardsley's in September 1990, before Javier Hernandez headed an injury-time consolation - but there were many more who deserved the plaudits.
Tireless livewire Luis Suarez had a hand in all three goals while Lucas Leiva and Raul Meireles produced impressive midfield performances. The afternoon was capped off with a long-awaited debut for record signing Andy Carroll after more than two months on the sidelines with a thigh injury.
For United their second-choice central defensive partnership of Wes Brown and Chris Smalling never looked comfortable on an afternoon when very few of visiting team reached anywhere near the exacting standards Ferguson demands, while Nani departed the action on a stretcher in the first half.
They still remain top of the table, and it is difficult to bet against them being in that position come May, but two defeats in five days - having lost at Chelsea in midweek - leave plenty of questions to be answered.
Source: PA
Source: PA