Ten-man Manchester United piled the pressure on Kevin Keegan as they emerged victorious from a high-octane derby-day FA Cup encounter with City.

Inspired by demanding skipper Roy Keane, United made light of the first dismissal of Gary Neville's career before the interval to score three times in an amazing second half.

Ruud van Nistelrooy took his seasonal tally for United to 24 with a close-range brace, with Paul Scholes and Cristiano Ronaldo also finding the net.

Michael Tarnat and Robbie Fowler were on target for City, who were denied on four occasions by Tim Howard and wasted three glorious chances to give the hosts a nervy last couple of minutes.

For half an hour the encounter was muscular rather than spectacular.

Neither side were willing to give ground in central positions, although as time went on Keane and Phil Neville gained the ascendancy as United took control.

Tarnat was finding it increasingly hard to contain Ronaldo. The young Portuguese winger went close with a header, as did Keane, before he sent a free-kick dipping narrowly wide of Arni Arason's goal.

Arason did well to save Keane's close-range effort after the Irishman had run onto van Nistelrooy's lay-off and with United doing most of the pressing as the half-hour mark passed it was no real surprise when Scholes put them in front.

Claudio Reyna had looked favourite to reach Ryan Giggs' low cross but the American, fearing he was about to turn the ball into his own net, hesitated and Scholes slid in to poke the ball home.

Even though Fowler was toiling away at the other end whenever City launched one of their sporadic attacks, it was difficult to see where the visitors were going to get a goal from until the game erupted with Neville's dismissal.

The England full-back could have no complaints about the red card brandished in his face by referee Jeff Winter for a clear head-butt on McManaman and, when he looks at television replays, he would also be wise to concede the official was right to reject the penalty claims that preceded it when he theatrically went down under pressure from Tarnat.

What annoyed the United contingent was that Steve McManaman escaped without punishment even though it was the former Real Madrid man who raced towards Neville to start the rumpus in the first place and also instigated the head-rubbing which his opponent took too far.

Joey Barton was yellow-carded for his part in the melee that followed and when the dust settled, City, with the extra man, emerged as the stronger force.

Howard denied Fowler with a feet-first save just before the interval, then turned away a Shaun Wright-Phillips strike after the restart when the England Under-21 star was well placed to do far better.

If those two saves were in the top-class category, the one the American produced to block a point-blank Barton volley after Antoine Sibierski had nodded Richard Dunne's cross into the six-yard area will struggle to be beaten all season.

Calling on all their vast experience, United tried to keep a calmness about their play, using Ronaldo's pace to counter-attack wherever possible.

Van Nistelrooy had a more plausible penalty claim turned down when he tumbled under Sylvain Distin's challenge.

By now though Howard was by far the busier goalkeeper, holding on to McManaman's underhit volley wide after Fowler flicked a pass to his good friend 10 yards out.

Out of all the chances City had created, it was probably the worst miss and proved to be extremely costly as, on their next attack, United doubled their lead and tripled it on the one after that.

The second owed much to van Nistelrooy's predatory instincts as the prolific Dutchman stole in at the far post to meet Ronaldo's deep cross.

City were still catching their breath when Quinton Fortune darted past Dunne to the byline and cut a cross back to Giggs.

Arason did well to turn the shot away but it dropped straight to Ronaldo, who sent the rebound flying into the net.

Still the scoring was not finished as Tarnat smashed home for the visitors 12 minutes from time.

Having come back from three goals down in the previous round at Tottenham, it raised hopes of another rousing fightback.

Instead it brought a fourth for United as Keane sent a far-post Giggs cross back into the six-yard area where van Nistelrooy bundled it in.

Fowler pulled another goal back for the Blues with a quickly-taken free-kick but the former England man shot wide and Sibierski twice wasted golden opportunities to give United a late scare.

Teams

Manchester Utd: Howard, Gary Neville, O'Shea, Silvestre, Fortune, Ronaldo, Phil Neville (Brown 90), Keane, Giggs (Butt 88), Scholes, van Nistelrooy.

Subs Not Used: Carroll, Forlan, Fletcher.

Sent Off: Gary Neville (39).

Booked: Gary Neville.

Goals: Scholes 34, van Nistelrooy 71, Ronaldo 74, van Nistelrooy 80.

Manchester City: Arason, Van Buyten, Dunne, Distin, Tarnat, Wright-Phillips, McManaman, Reyna, Barton, Sibierski, Fowler.

Subs Not Used: Stuhr-Ellegaard, Wiekens, Macken, Bosvelt, Elliott.

Booked: Tarnat, Barton.

Goals: Tarnat 78, Fowler 86.

Att: 67,228

Ref: J Winter (Cleveland).