The FA Cup dream is over but United came away from the Riverside with heads held high after Middlesbrough netted a fortunate extra-time winner.

In front of the TV cameras, the Blades held their Premiership opponents for more than 200 minutes in the fifth round tie before the home side accepted a great slice of luck.

Mido's shot took a deflection off Chris Morgan and the ball came back off a post before striking Paddy Kenny and trickling over the goal-line in the second period of extra-time.

Speed returned as boss Blackwell's only change from the weekend's draw at QPR. The experienced midfielder took the place of Armstrong, who dropped to the bench to join former Boro defender Ehiogu. The home side handed a full debut to £12m Brazilian striker Alves but were without suspended duo Wheater and Aliadiere.

It was quickly apparent that Quinn had been moved out to the left to accommodate Speed and it was United that had most of the territorial advantage in the first five minutes.

Boro, however, looked dangerous when Downing delivered for Mido, but Kilgallon cleared. Then, on six minutes, Rochemback swung in a free-kick and Hines headed over after getting in ahead of Kenny.

The home side were getting on top - despite Beattie's appeals for a penalty when he was held back by Pogatetz - and from the first corner, by Rochemback, an unmarked Alves glanced a header wide, whilst Downing danced in from the left and fired wide with his weaker right foot.

Boro fans were visibly excited to see Alves pick up the ball and run at the defence on 17 minutes but his movements were tracked by Morgan, who provided the block. A moment later, with United on the attack, Naysmith's cross from the left took a deflection and gave Beattie little time to react, despite the striker taking up a good position.

Downing was quite active in Middlesbrough's attacks and on 24 minutes his pace almost brought the opening goal. He carved through the Blades defence with pace, played a one-two with Rochemback, and then dragged his shot wide, again with his right foot. The England winger, however, used his favoured left foot soon after to deliver a corner, from which Pogatetz glanced wide.

Although United were having a fair share of possession, chances were limited and the home side were forcing saves from Kenny. On 35 minutes, after he was hauled down, Alves struck a powerful free-kick, which the goalkeeper punched away and then Rochemback tried his luck from long distance.

From Beattie's cross Hines and Schwarzer got themselves in a tangle but again Boro hit back and after Alves got the better of Kilgallon, Young's close-range effort was kicked away by Kenny.

As well as plenty of chances, the first half was also littered by a number of bookings - two from each side - and fouls, whilst the final effort of the half was a Stead shot on the turn following Tonge's cross.

The start of the second half was interrupted by a head injury to Morgan, but the Blades skipper was soon back into the action, again blocking as Alves looked to work an opening. Sharp won the first corner of the half from Hines but Boateng headed clear.

Lifted by their crowd, Boro were soon back on the attack, winning a number of corners, whilst Beattie was forced to clear, under pressure, following an inswinging free-kick by Rochemback. On 65 minutes, a breakaway by Arca gave Alves a shooting chance but the subsequent strike was comfortable for Kenny, dropping to his left.

The penalty box action continued with Schwarzer flapping at a free-kick and Quinn and Martin attempting to hook the ball back towards goal, whilst at the other end there were half-hearted appeals for a spot-kick when Kilgallon challenged Alves.

As the last ten minutes approached, United's travelling contingent continued to offer vocal support, whilst both managers threw on substitutes in hope of snatching a late winner. Boateng attempted to get on the end of a Downing cross but he was put under pressure by Naysmith.

In the last five minutes Martin and then Geary threw their bodies on the line to block from Boateng and Downing respectively, but, perhaps, the best chance of the night came in the final minute. Following a corner, Speed and Martin hooked on for Beattie to get in ahead of Schwarzer but the striker's stab was just wide of the target.

Kilgallon won a couple of vital headers in the three minutes of injury-time, whilst Boro were unable to find the target with two late corners and a free-kick, meaning extra-time was necessary.

Blackwell was forced to use his final substitution at the start of the extra period with Martin hobbling off just half an hour after being introduced. Shelton was the replacement.

Boro began extra-time well and on 92 minutes Downing found space on the left but fired a yard wide from the edge of the box.

Kenny excelled on 97 making a fine double save after Quinn surrendered possession. Firstly, the goalkeeper saved with his legs after Downing's shot deflected off Morgan and then he covered his near post well when Tuncay looked for an opening.

Shelton's cross deflected off Young and caused a problem for Schwarzer, but the goalkeeper adjusted and the final chance of the first period of extra-time saw Young fire well over the crossbar.

Johnson fizzed the ball across the goalmouth early in the second period and Downing was unable to get a decent connection on Young's cross.

The decisive moment arrived on 112 minutes and Middlesbrough can count themselves fortunate for a number of reasons. Firstly, a hopeful ball into the box took a couple of ricochets before landing at the feet of Mido. Then, the Egyptian's shot took a massive deflection off Morgan to rattle a post and the ball struck the arm of Kenny before trickling over the line.

Tuncay and Johnson looked for a second but were both off target and Kenny looked to make amends by racing forward for a late free-kick but was unable to affect the play and in the end Beattie raced the length of the field to make a telling tackle on Tuncay.

Two minutes extra-time was played by referee Walton but United's hopes of a quarter-final against Cardiff ended when Pogatetz made a last-ditch block from Kilgallon.

Boro: Schwarzer, Young, Arca (O'Neil 77), Pogatetz, Boateng, Mido, Rochemback (Johnson 104), Alves (Tuncay 73), Downing, Hines, Grounds.
Unused: Turnbull, Cattermole.

Blades: Kenny, Naysmith, Morgan, Beattie, Stead (Martin 59, Shelton 90), Speed, Kilgallon, Tonge, Sharp (Hulse 73), Geary, Quinn.
Unused: Armstrong, Ehiogu.