Liverpool came from behind to hit four goals at Old Trafford and reduce the gap at the top of table on a miserable day for the champions who also had Nemanja Vidic sent off.
Manchester United 1-4 Liverpool
Both sides made changes for the hotly-anticipated clash, Carlos Tevez replacing Dimitar Berbatov for the champions who also included Anderson and Park Ji-Sung in their starting line-up at the expense of Ryan Giggs and Paul Scholes.
Liverpool, meanwhile brought in Lucas Leiva for the injured Xabi Alonso and were also forced into a late change with Sami Hypia coming in for Alvaro Arbeloa after the Spaniard suffered a hamstring injury in the warm-up.
United began the game brightly and with only three minutes on the clock had opened up Rafael Benitez’s side.
Carlos Tevez out on the right squared a ball to Park inside the box who looked to shoot but his effort was blocked and flew over the bar after a vital challenge by Jamie Carragher.
After a slow start Liverpool quickly warmed to their task with skipper Steven Gerrard once again urging his side forwards.
With only 10 minutes gone the skipper burst inside the box before trying to cut inside Nemanja Vidic but the Serbian did well to deny him sight of Van der Sar’s goal and clear the danger.
Yet Liverpool’s other talisman Fernando Torres was also causing problems in the usually unflappable United defence.
The Spaniard showed superb skill to turn inside Rio Ferdinand and weave into the box but he needed an extra touch to surge past John O’Shea which just allowed Vidic to clear.
A game that had been slow to get going was beginning to warm up nicely and mid-way through the first-half Old Trafford saw its first goal.
A super ball by Tevez inside Carragher and Hypia found Park inside the box. The Korean latched onto the ball but Reina came out quickly to deny the United man but only succeeded in bringing him down and conceding a penalty.
Up stepped Cristiano Ronaldo who calmly slotted his kick past the Liverpool keeper to hand his side the lead.
The goal filled the home side with confidence but it was short-lived as a mistake by none other than Nemanja Vidic ensured that United’s advantage lasted only five minutes.
A long ball upfield by Martin Skrtel was badly misjudged by the centre-back who allowed the ball to bounce over his head.
Facing his own goal the Serbian was then beaten to the ball by Torres who advanced on goal before slipping the ball effortlessly past Van der Sar.
United looked stunned but were quickly back in action at the other end as they sought to re-establish their lead.
Tevez almost profited from a moment of indecision from Reina, after the Spaniard fumbled a Ronaldo free kick, before Michael Carrick thrashed a shot inches over the bar.
Yet at the other end Torres was looking a real threat for the Reds and only minutes before half-time there was to be even more drama in an already action-packed first period.
A splendid ball from Torres into the United box saw Patrice Evra upend Gerrard and once again referee Alan Wiley showed no hesitation in pointing to the spot.
Skipper Gerrard dusted himself down to take the kick and planted it past Van der Sar to hand the Reds a priceless lead at the interval.
A grim-faced United emerged from the break and within minutes had hit the post. A right-wing cross from Ronaldo took a deflection and Reina could only watch as it rattled his near post before grabbing it gratefully.
Ten minutes later and a Tevez cross again had Reina struggling before, back-pedalling, he just managed to tip it over his bar.
United were dominant and were only inches away from grabbing an equaliser on the hour mark.
A Ronaldo cross to the far post found Rooney guiding the ball back to Tevez right in front of goal but Skrtel did just enough to deny the striker from close range.
Yet in truth United were struggling to penetrate a Liverpool side happy to defend their lead and, with time ticking away, Sir Alex made a triple substitution sending on Berbatov, Giggs and Scholes for Anderson, Carrick and Park.
However, minutes after the substitution and Manchester United found themselves down to 10-men after Vidic was sent off for hauling back Gerrard as he surged goalwards.
From the resulting free-kick Fabio Aurelio lifted a brilliant effort over the wall and low into the corner of Van der Sar’s goal to seal victory.
Yet there was still time for even more joy for the visiting side. Another long ball forward found substitute Andrea Dossena lifting a neat finish over Van der Sar as United shipped four goals on a day their lead at the top was also cut to just four points.
Manchester United: Van der Sar, O'Shea, Ferdinand, Vidic, Evra, Ronaldo, Carrick (Scholes, 74), Anderson (Giggs, 74), Park (Berbatov, 74), Rooney, Tevez.
Liverpool: Reina, Carragher, Hypia, Skrtel, Aurelio, Mascherano, Lucas, Kuyt, Gerrard (El Zhar, 90), Riera (Dossena, 68), Torres (Babel, 81).
1-4 Liverpool (Dossena, 90 + 1)
1-3 Liverpool (Aurelio, 76)
1-2 Liverpool (Gerrard, pen 44)
1-1 Liverpool (Torres, 28)
1-0 Manchester United (Ronaldo, pen 23)
Gill Clark, Goal.com