Manchester United 4 Manchester City 2: Gary Neville should be grateful to the generosity of the team he despises.

Safely navigating a route to the quarter-finals will only partially have diluted his shame for jeopardising this victory but the most acute suffering belonged to those of a Manchester City allegiance and, specifically, their manager whose 53rd birthday might have propelled him closer to an early retirement.

Nothing more can be said about Neville's assault on Steve McManaman that will cut to the bone as much as the volcanic criticisms of Alex Ferguson and, maybe even worse, the guilt that accompanies letting down the club he cherishes. The second red card of Neville's career will be punished with a three-match ban and a fortnight's docked wages. But such measures will feel mild compared to the wretchedness that would have engulfed this student of Manchester's sporting enmity had Kevin Keegan's players been suitably equipped to accept what he described at half-time as "the best opportunity you'll ever get at this ground".

An illusion has been formed by the fact that City created so many chances. The profligacy of a team should be an indictment rather than a consolation, particularly against a side with a numerical disadvantage, and Keegan should not comfort himself that, along with Roy Keane and Cristiano Ronaldo, Tim Howard was the hosts' outstanding player. True, Howard did underline his position as the Premiership's outstanding goalkeeper but how many were bad misses and how many were great saves? While Paul Scholes, Ruud van Nistelrooy, twice, and Ronaldo demonstrated United's merciless streak, all their goals coming from inside the six-yard area, their opponents cannot count ruthlessness as one of their virtues.

McManaman, Antoine Sibierski and Shaun Wright-Phillips shared the culpability and, when City did apply an incisive edge, Michael Tarnat spearing a shot into the roof of the net and Robbie Fowler catching out Howard with a quickly taken free-kick, it scarcely mattered given that they were three goals behind on both occasions.

"I'm extremely annoyed with myself," said McManaman. "You look back at the chances we've missed and the goals they've scored and you cringe. It's not as if we've been beaten by a fantastic team who have come at us with wave after wave of attack." Not in the second half anyway. Until Neville's rush of blood United had been coasting, with their opponents yet to mount a meaningful attack, and it emphasised the difference between the sides that Ferguson's men still added another three goals after they had been pressed into methods of containment.

"They scored from half-chances and we missed gilt-edged chances," said Keegan. But there were other contributing factors. For starters Keane's mood was of such defiance that, with the score at 4-1, he could still be found bullying the ball off Daniel van Buyten, instigating a move from which Van Nistelrooy could have scored his hat-trick.

Van Buyten's vulnerability was a theme of City's defence while the impressive work completed by McManaman and Joey Barton in midfield was tempered by the ineffectual Claudio Reyna. Keegan will be disappointed, too, that Wright-Phillips did not pose the same difficulties for Quinton Fortune as those Tarnat encountered trying to control Ronaldo.

As for Neville, there is little in the way of mitigating circumstances. Allegations of manipulating a penalty claim may amount to one of the worst kind of insults but his sympathisers will struggle to mount a defence for the headbutt on McManaman.

"We've been together with England countless times and there has never been any history between us," said McManaman. "I was just unhappy with the way he went down and after that it was a load of nonsense. As far as I'm concerned it's over." Sadly for City, the same might be said for the aspirations of their present management. "I'll see you next week," was Keegan's parting shot but there are increasingly legitimate reasons to doubt his long-term suitability to a job that is proving beyond him. All City have now is a relegation battle and, whatever happens, Keegan must feel he has failed.