Derby County 1 Manchester United 4:MANCHESTER UNITED have won so many games 1-0 recently that the football world might have been duped into thinking they had brought in a new code of conservatism. If so, we should probably have known better. Alex Ferguson takes pride from nurturing the most adventurous team in the land and his players put on a performance here that made it seem as though they were affronted by the suggestion they had lost the ability to scintillate.

Derby can console themselves with the fact that, courtesy of Miles Addison’s 56th-minute header, they showed that United’s record-breaking defence is not so impenetrable when the goalkeeper, Edwin van der Sar, and Nemanja Vidic are rested. But they would be clutching at straws. By then Nigel Clough’s team were 3-0 down to goals from Nani, Darron Gibson and Cristiano Ronaldo and normal service resumed when the substitute Daniel Welbeck curled in United’s final goal with nine minutes to go.

All this came from a side with no recognised centre-forward in the starting line-up. It was an epic, lyrical performance, full of everything that is good about Ferguson’s team and a reminder that “genius” is not too strong a word to describe Ryan Giggs’s gifts.

Giggs is 34 now, reaching the stage of his career when insecurity can appear on the horizon, but his left foot has gone beyond the stage of being described as “educated”. A master’s degree is surely called for, given the finesse of his touches.

Gibson is not so refined but an honorary mention should also go to the Republic of Ireland international, while Darren Fletcher, Nani, Park Ji-sung and the rest of the supporting cast ensured this was a chastening experience for their opponents.

The remarkable thing was that Ferguson ensured some of his more important players did not even muddy their knees. You have to admire the manager’s chutzpah in leaving out Carlos Tevez and Dimitar Berbatov when Wayne Rooney was already missing through injury. But Ronaldo scores goals like a centre-forward anyway, as demonstrated three minutes into the second half when he powered a header past Stephen Bywater from Giggs’s corner.

United’s noisy supporters had turned this into a 1970s-themed day, with their retro banners and scarves, and this was a header that Joe Jordan would have been proud of. Ronaldo would have been on the scoresheet even earlier had it not been for the most confusing moment of the day when the referee’s assistant, Paul Tierney, decided United’s most prolific player had been offside from Giggs’s exquisite flick. The delicacy of Giggs’s touch was, it turned out, too subtle for Tierney to notice, and he took so long making up his mind Ronaldo had accepted all the congratulations and was trotting back for the restart by the time the flag was raised.

The score was 1-0 at the time and, in the unlikely event of a Derby comeback, Tierney’s punishment would undoubtedly have been an infamous place in FA Cup lore, especially as Jordan Stewart had been playing Ronaldo onside regardless of whether or not Giggs touched the ball.

But United quickly set about extinguishing the first flames of controversy. A minute before half-time Ronaldo’s free-kick spun off the defensive wall and Gibson volleyed low and hard to Bywater’s left. The shot went under Rafael da Silva, who was in an offside position, but Tierney was so perplexed at this stage he ruled, wrongly, that the Brazilian was not impeding Bywater’s view.

This was a day, however, to admire United’s football rather than chastise the officials. And the imbalance of talent was such that there was only one brief flurry – after Addison had headed in Kris Commons’s cross – when the Championship side worked up a head of steam. That apart, there was an inevitability about which team would reach the quarter-finals from the moment Nani cut inside Paul Connolly and scored with a swerving right-foot drive from the edge of the penalty area.

For Derby an improbable recovery could have been feasible had Ben Foster, deputising for Van der Sar, not produced a fine save to keep out Gary Teale with the score at 3-1. Instead United broke forward again, Fletcher set up Welbeck and the teenager confidently buried his shot.

• Guardian Service