Giggs, all touch and vision, was again magnificent. Nani and Ronaldo, such elusive scarlet pimpernels, both scored while United's phenomenal strength in depth was confirmed in well-taken goals by Darron Gibson and Danny Welbeck. Amid all this shimmering beauty lurked a real ruthlessness. United fans are loving it. They had clearly been busy with the sewing machines, creating banners to go with their chants. All Singers and songs, United's following filled the South Stand with messages, saluting everyone from Carlos Tevez to Nemanja Vidic. 'The fans were fantastic," said Sir Alex Ferguson.
One banner stood out – 'Marching to Wembley". If they win at either Swansea or Fulham in the quarter-finals, United will be guaranteed another Wembley appearance to go with their Carling Cup outing (as the FA Cup semis are staged under the famous arch).
United's vaulting ambitions appears unstoppable. Nigel Clough's Derby, neat and nimble in their new master's image, performed well despite the painful-looking scoreline. They have now struck four times against United in 39 days, a miracle as no Premier League side has breached the champions' backline since Nov 8, yet they have nothing but pride to show for their energetic labours.
Ferguson's men were simply a class apart. Clough even suggested 'it is possible" that United could lift the Champions League and the three domestic trophies because of the 'quality" and depth of their squad.
Gibson was just starting school in Derry when Giggs began weaving his magic in a red shirt, and the young midfielder impressed in the centre here. 'Gibson did really well," said Ferguson. 'He has got into the Carling Cup final team with that performance."
Ben Foster exuded calm in goal, making some good clearances, and having no chance with Miles Addison's second-half header. Welbeck raced on and scored as United made light of Tevez remaining on the bench and Wayne Rooney and Dimitar Berbatov staying at home. 'Welbeck is a natural finisher," added Ferguson.
Clough smiled ruefully afterwards when asked how a manager could prepare for opponents blessed with so many options. 'It's almost impossible," said the Derby manager. 'Giggs has played wide [against West Ham], central midfield [against Chelsea] and through the middle [yesterday]!"
Giggs was partnered by Ronaldo, whose acceleration constantly worried Clough's centre-halves, Addison and Martin Albrechtsen. 'He's an option for us as a striker but I prefer him as a winger," said Ferguson of Ronaldo. 'He gets so many goals from the wide areas, and we've got Tevez, Berbatov and Rooney (in the centre)."
Even with so many understudies in the United ensemble, a familiar drama was again staged – the turning of the screw. Outclassed, Derby were far from overawed, Robbie Savage quickly lecturing Ronaldo for going down too easily under one of his challenges. Savage loved this tussle, yet Ronaldo was almost untouchable at times.
United's threat grew and only Stephen Bywater's reflexes kept them at bay. First he saved from Darren Fletcher, then Ji-sung Park. Yet Derby gave their noisy fans plenty to sing about. Kris Commons buzzed about. Rob Hulse volleyed over and then appealed in vain for a penalty when challenged by Rio Ferdinand. The eye kept being drawn back to Giggs, 35 going on 25. Awarded a new one-year contract, Giggs would certainly not have been flattered by a three-year deal on this vibrant evidence. He helped make United's first, combining with Park, Gibson and Fletcher to set up Nani, whose 20-yarder flashed past Bywater.
A font of creativity, Giggs then flicked a pass through the middle for Ronaldo to chase and swiftly pace past Bywater. As United celebrated, the linesman Paul Tierney signalled to the referee Alan Wiley and a brief pow-wow broke out. Tierney asked Wiley whether Giggs had touched the ball, which he had so the linesman insisted that Ronaldo was offside. Strange. Jordan Stewart appeared to have played him on.
No matter. United soon had their second. When a Ronaldo free-kick bounced kindly off the Derby wall to Gibson, the midfielder sent it racing past Bywater. Wiley should have ruled this one out as Rafael, running across the box, interfered with the keeper's vision.
United were really flying now, adding a third shortly after the break. When Stewart, trying to shepherd the ball away from Park, needlessly conceded a corner, United took full advantage. As Giggs curled the ball over, Ferdinand's decoy run created space. Ronaldo darted in and headed powerfully past Bywater. For a while, United put on the Ritz, Ronaldo even attempting to score with a back-heel from 15 yards. All the while, Giggs' passing touched the sublime. Derby refused to bow out meekly. Gary Teale began creating trouble down the left, lifting in a cross that Foster did well to punch away. United's keeper was beaten after 55 minutes. When Savage stroked the ball down the right, Commons crossed for Addison to place his header wide of Foster.
Any thoughts of a Derby comeback were always going to be far-fetched, particularly with Giggs directing operations for United. The Welshman conducted a one-two with Fletcher on the edge of the area and Welbeck applied the coup de grace.
United's attention now turn to the Premier League. The champions will go five points clear if they defeat Fulham. 'Everyone will be ready for Wednesday," said Ferguson. 'I rested Tevez with that game in mind. Rooney should be ready for Saturday – it might be Wednesday but definitely Saturday." Who can catch football's Red Arrows?