United staged a massive smash and grab raid at Anfield, surviving the late dismissal of Paul Scholes to snatch all three points through an injury-time John O'Shea strike.
The big Irishman, on as a substitute for the injured Wayne Rooney, smashed home the loose ball after Liverpool goalkeeper Pepe Reina had parried Cristiano Ronaldo's free kick.
Sir Alex Ferguson's side adopted an extremely cautious approach for the massively important clash, posing the hosts almost no attacking threat, and got their rewards with an invaluable victory in this year's title race.
Edwin van der Sar and Rio Ferdinand in particular were in inspired form, coping admirably with the dual threat of Dirk Kuyt and Craig Bellamy.
A relatively tepid first half saw Liverpool create the majority of the chances, but United's wastefulness in attack saw a host of promising openings spurned.
Cristiano Ronaldo had United's best chance, lashing over after a breackneck, incisive move involving Gary Neville and Henrik Larsson.
John Arne Riise was responsible for the hosts' best moment, smashing a free kick just wide of Edwin van der Sar's upright.
Following a poor first 45 minutes, Liverpool flew out of the traps after the interval, as first Gerrard lashed wildly over the bar before Bellamy forced van der Sar into his first save of note.
The Welsh striker latched onto Kuyt's through ball, but was thwarted as the big Dutchman clawed away his low effort.
Bellamy thought he had opened the scoring shortly afterwards, but was correctly ruled offside after he converted Sissoko's flick from close range.
