Liverpool's supporters started the day being taunted by a bunch of opportunists who escaped Old Trafford's security blanket to re-enact Diego Forlan's Anfield match-winner. It proved to be the highlight of their afternoon.

After coming to terms with Karl Power's latest scam, the visiting fans then learned of the absence of Michael Owen and finally found out their captain was going to miss most of the game as well.

Unfortunately for Sami Hyypia, he had started it, his brief appearance brought to an end by the red card brandished in the Finn's face by referee Mike Riley for his clumsy fourth minute foul on Ruud van Nistelrooy.

At the start of a period neatly summed up as 'make or break' by manager Sir Alex Ferguson, it was precisely the turn of events United were looking for.

As Hyypia slunk away down the tunnel, he will have heard the roars of the Stretford End above. Van Nistelrooy just doesn't miss penalties.

Gerard Houllier hastily re-organised, with unlucky Milan Baros the man sacrificed on the altar of defensive stability, and for an hour they clung on, only for their world to collapse without warning in as United romped to their biggest win in the fixture for half a century.

Given their early lift, and the prospect of Tuesday's tussle in Madrid and the battles with Newcastle and Arsenal still to come, it wasn't too great a surprise that the home side didn't press their collective foot hard on the throttle.

With David Beckham nursing a slight cold on the bench, the home side lacked an ability to deliver a killer cross, even if his replacement Ole Gunnar Solskjaer was their most effective offensive player.

Jamie Carragher and Djimi Traore cleared a couple of dangerous balls into the box and Mikael Silvestre volleyed into the net, only for the goal to be ruled out for an obvious foul on Jerzy Dudek in the build-up.

The villain of the first meeting between the sides at Anfield - and the butt of Power's prank - Dudek atoned for that performance which an outstanding display with saw Liverpool capture the Worthington Cup at their rivals' expense in Cardiff at the beginning of last month.

Despite United's man advantage though, Dudek wasn't called upon as often as he was at the Millennium Stadium. Liverpool offered little in attack but had succeeded in dragging their opponents to a level which suited the visitors more and which brought an interval reminder from Ferguson to quicken the tempo.

This they duly did, yet still the second wouldn't come, Van Nistelrooy coming closest when he just failed to touch home Solskjaer's cross-shot.

Then suddenly, it all went horribly wrong - or right depending on which side of the red fence you sit.

Hyypia's replacement Igor Biscan found himself in the wrong place at the wrong time, blocked off Paul Scholes the England man attempted drive into the penalty area after taking Roy Keane's square pass and United were given their second spot-kick.

Van Nistelrooy's tactic in these situations is a simple one. Keep your head down and hit the ball as hard as you can, mostly to the goalkeeper's right. Dudek knew what was coming, stopping it is another matter.

The Dutchman now has 34 for the season, just two behind last year's tally and with the tests to come, Ferguson will hope the knock Van Nistelrooy took late in the game doesn't turn into a major problem.

After such stoic defending, Liverpool stared at the scoreboard, remembered the imbalance in numbers and fell apart.

Beckham's entrance gave the home side an extra attacking option and when he swung in a trademark inswinging cross from the right, Giggs slid in to convert his first Premiership goal at Old Trafford for over three years.

The misery wasn't over for Liverpool. Four years ago, Solskjaer scored an injury-time goal at the same ground to knock them out of the FA Cup. His execution came at roughly the same time today, although with admittedly fewer consequences, other than to turn the visitors' faces a deeper shade of red.

On Grand National day, United have negotiated one difficult obstacle. Football's equivalent of Beecher's Brook is now looming into view.

Teams

Man Utd: Barthez, Gary Neville, Ferdinand, Brown, Silvestre (O'Shea 66), Solskjaer, Keane, Phil Neville (Beckham 66), Giggs, Scholes (Butt 79), van Nistelrooy.

Subs Not Used: Ricardo, Forlan.

Booked: Silvestre.

Goals: van Nistelrooy 5 pen, 65 pen, Giggs 78, Solskjaer 90.

Liverpool: Dudek, Carragher, Hyypia, Traore, Riise, Diouf (Smicer 71), Hamann, Gerrard, Murphy (Cheyrou 80), Heskey, Baros (Biscan 6).

Subs Not Used: Arphexad, Mellor.

Sent Off: Hyypia (4).

Booked: Diouf, Murphy, Gerrard.

Att: 67,639

Ref: M Riley (W Yorkshire).