Sir Alex Ferguson's FA Cup love affair ended in disaster at Middlesbrough as the Barclaycard Premiership strugglers sent the champions packing.

Ferguson would have dearly loved to see his side lift the first trophy he ever won as United boss once again in his final season in charge, but those dreams were blown apart in a remarkable finish to a topsy-turvy afternoon on Teesside.

The visitors, who left Ruud van Nistelrooy and Ryan Giggs on the bench and the injured David Beckham and Juan Sebastian Veron at home, dominated the first half to such an extent that Boro boss Steve McClaren was forced to completely change the shape of his side at the break.

But Ferguson's former lieutenant got it just right in the second half to turn the tables on the man who snatched Uruguayan striker Diego Forlan from his grasp last week.

Goals from Noel Whelan - his fourth in seven games - and substitute Andy Campbell inside the last five minutes gave the Teessiders a famous victory and sent home the Boro fans in a paltry crowd of 17,624 with the perfect reward for their loyalty.

Individual mistakes from French duo Laurent Blanc and Fabien Barthez created the opportunities for the Teessiders, but that took nothing away from the quality of the finish in either case.

However, it could all have been so different had midfielder Robbie Mustoe not headed off the line from Ronnie Wallwork before the break and then taken a Mikael Silvestre header on his chest in the second half in a similar position.

A Boro side robbed of the services of skipper Paul Ince through suspension and defender Ugo Ehiogu and leading scorer Alen Boksic through injury, showed just the courage and tenacity they will need to climb out of the relegation zone to book their place in the fifth round.

But few in the crowd would have put any money on the Teessiders running out winners as they got to half-time by the skin of their teeth still hanging on to a clean sheet.

That they did so was down to a combination of superb defending by England international Gareth Southgate and a lack of cutting edge from their opponents, who teamed up Ole Gunnar Solskjaer and Paul Scholes in a makeshift frontline.

Mustoe's clearance from Wallwork's 11th-minute header set the alarm bells ringing and Solskjaer only just failed to connect with Silvestre's tempting cross on 29 minutes.

But goalkeeper Mark Crossley was otherwise largely a spectator despite the visitors controlling the game from the middle of the field through the hugely influential Roy Keane and Wallwork.

Boro registered the first shot 41 minutes into the game and their second a minute later, but neither Whelan nor the combative Dean Windass could force Barthez even to raise an eyebrow.

McClaren, who has found himself under increasing pressure in recent weeks, arrived from Old Trafford with a reputation as one of the country's top emerging coaches, and he proved his worth at the break as his mind went into overdrive.

Off came the largely ineffectual Carlos Marinelli and Allan Johnston as Jason Gavin was sent on to bolster the defence and former Manchester United midfielder Mark Wilson was thrown into a three-man midfield.

The move paid dividends almost immediately as Wilson, Robbie Stockdale and Windass tested Barthez in quick succession as the home fans sensed the game might not develop into a procession after all.

They were on their feet again on 56 minutes when a Colin Cooper free-kick looped up off Windass and sailed inches wide, although they were swiftly served with a reminder of United's potency when Paul Scholes wastefully drove wide at the other end after Keane had opened up the Boro rearguard.

Mustoe's second last-ditch intervention to deny Silvestre on 67 minutes increased belief that this could be McClaren's day, and the sensation began to grow as even substitutes Giggs and van Nistelrooy could not beat Crossley.

However, few would have predicted the stunning finale which finally decided the tie.

Crossley's long 85th-minute free-kick was going nowhere until Blanc inexplicably allowed the ball to drop over his head, where an astonished Whelan kept his cool before slotting past the helpless keeper.

Boro cut their celebrations short to batten down the hatches as the seconds ticked away, but when Barthez made a hash of a late clearance, Whelan fed the ball out to Windass and he crossed for the Campbell, who had forced the initial error, to head home.

It was the Stockton-born striker's first senior goal in 21 months after an injury nightmare which cost him a proposed move to Crystal Palace, but many a Boro fan will drink a toast to his name this evening as they celebrate a fairytale day at the Riverside.

Teams:

Middlesbrough: Crossley, Southgate, Cooper, Queudrue, Stockdale, Greening, Mustoe, Johnston (Gavin 45), Marinelli (Wilson 45), Windass, Whelan, Wilson (Campbell 75).

Subs Not Used: Beresford, Ricard.

Booked: Stockdale, Cooper, Greening.

Goals: Whelan 85, Campbell 89.

Man Utd: Barthez, Gary Neville, Blanc, Phil Neville, Silvestre, Wallwork (Giggs 61), Keane, Butt, Chadwick (van Nistelrooy 61), Scholes, Solskjaer (Yorke 79).

Subs Not Used: Carroll, O'Shea.

Booked: Wallwork, Silvestre, Scholes.

Att: 17,624

Ref: M Halsey (Welwyn Garden City).