Northampton -0 Manchester United - 3:English FA Cup/Fourth round: Romance gave way to reality here last night. For all that there was the odd heart flutter en route, whipped up by spirited if limited opponents, Manchester United's passage into the fifth round was secured with plenty to spare.

Only profligacy and the excellent Lee Harper denied the visitors a more emphatic victory, though so comfortable in truth was their success that United's wastefulness might have been explained away as a desire not to spoil the Cobblers' big day.

Northampton Town, underachieving in the third division's lower mid-table, could take much from this performance but they never threatened to glean an upset.

"The annoying thing is that the goals we conceded were all so sloppy," grumbled Colin Calderwood, his side's defeat tempered by the £400,000 payday which should help secure the purchase of this stadium and its surrounding land from the council over the next month.

"Premier League sides find it hard playing United, yet their football is so simple. The speed and rhythm of their passing, the width to their game - it was a lesson for us, really."

An awkward opening aside, victory was simple. That the visitors sauntered in with virtually a reserve side on the final whistle, and boasting an average age of barely 22, said much for their dominance.

The three goals may have been uncharacteristically scrappy but there was a swagger to their play that the Cobblers failed to clobber. The own-goal prodded unwillingly home by Chris Hargreaves from Ronaldo's corner immediately after half-time doubled the Premiership champions' advantage and deflated home optimism.

The result was long beyond doubt by the time John O'Shea's cross was nodded down by the elusive Portuguese at the far post for Diego Forlan to poke in from close range.

United then cruised, the magnificent Paul Scholes withdrawn and Nicky Butt revelling in the captaincy, with their uncomfortable start gracefully exorcised.

Only in a frenzied opening quarter, when the livewire Derek Asamoah had tormented Mikael Silvestre, had Town threatened to unsettle the visitors, yet they still might have trailed early in that brief ascendancy.

Chris Carruthers was penalised for a third-minute push on Ronaldo at the far post, only for Forlan's lazy penalty to be palmed away magnificently by Harper.

The former Arsenal goalkeeper has now saved six spot-kicks this season and he will be sent the Uruguayan striker's shirt today as a memento.

"The floodgates would have opened if that had gone in," said Harper, who watched Asamoah dance on to his subsequent goal-kick only to see the Ghanaian's attempted lob cannon back off Roy Carroll and wide of the net. Though they later struck the woodwork twice when hopelessly adrift, that was as good as it got for the locals.

Parity was surrendered just after the half-hour.

Ronaldo, possibly emerging from an offside position, spat a weak cross-shot at goal which Harper would surely have gathered had the panicked Paul Reid not intervened, belting his attempted clearance against the prone goalkeeper with the loose ball ricocheting cruelly off Silvestre and dribbling in.

"In any tie there is always an element of worry and a possible banana skin," admitted Alex Ferguson, whose weakened selection was partly explained by a shin injury picked up by Ruud van Nistelrooy in Dubai.

"We had to scramble the ball away a few times and it is credit to Northampton for putting on a performance like that. I'll admit it was a big concern when the chances didn't go in."

United did eventually find their range - albeit thanks to Hargreaves's own-goal - with Harper later tipping Kieran Richardson's shot on to the crossbar and denying Forlan a second at full stretch. Yet further damage would have been harsh on the Cobblers.

As United relaxed, the Northampton substitute Marc Richards battered a breathless shot from the edge of the area on to the crossbar and in stoppage time Asamoah had a searing shot saved and could only slide the rebound onto the post.

"My boys kept going and can be proud of what they've achieved out there, but it's time to move on," said Calderwood. The Scot has Friday's league game with Doncaster Rovers to focus his mind; United have this afternoon's fifth-round draw.

"I watched Chelsea's game at Scarborough yesterday and I thought 'I can't go through that'. In FA Cup games like that there is always a chance that you may end up scrambling through. We didn't scramble today, we won comfortably," said Ferguson, who also defended his decision to field an almost unrecognisable line-up.

"We have European games on the horizon now and we have to be prepared for them. It is important to keep players playing. We got through, which is all that matters, but good luck to Northampton in the future," he said. ... Guardian Service