With United leading 1-0 and seemingly in total control, Fernando Torres and Steven Gerrard changed the game during a 20-minute period when they displayed all of their athleticism, intelligence and technical qualities.
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Talking tactics: Manchester United v Liverpool
Firstly the pace of Torres unsettled Nemanja Vidic into an error, which not only resulted in the Spaniard equalising, but also made United's defence drop deeper.
This then allowed Torres to utilise the space in front of the centre-halves to receive passes before sliding balls forward for the dynamic runs of Gerrard.
The foul in the area by Patrice Evra on Gerrard for Liverpool's penalty was reward for the inventiveness, positional rotation and awareness that both Gerrard and Torres displayed during that crucial period.
Ferdinand & Vidic
When United last lost in the Premier League, at Arsenal in November, Rio Ferdinand and Nemanja Vidic were below their best. Saturday was no different, because two of Liverpool's goals came as a result of Vidic's mistakes, with the second resulting in his dismissal.
Rarely have I seen Vidic look so cumbersome. Ferdinand was no better. Right from the outset he looked lethargic, both mentally and physically.
Liverpool's first goal could have been avoided had Vidic headed Pepe Reina's long kick, rather than letting it bounce behind him in the hope that someone else would deal with it.
Yesterday's poor performance emphasised just how important Vidic and Ferdinand's consistency has been to Sir Alex Ferguson over the last two years. If they cannot recapture their form quickly, United's chances of a clean sweep look unlikely.
Ronaldo & Rooney
Liverpool fans have yet to be convinced about the qualities of Lucas, but on Saturday he and Javier Mascherano performed their defensive duties superbly.
Not only did they get the better of their opposite numbers, Michael Carrick and Anderson, but they continually supported the full-backs whenever Ronaldo was running at them.
Lucas, in particular, stopped Ronaldo from drifting infield to hit shots, which ultimately rendered the Portuguese winger ineffective.
Rooney also found himself outnumbered whenever he picked up the ball in midfield and he became increasingly frustrated.