GOALFLASHES AND MAJOR INCIDENTS (all times BST)
1930: FULL TIME Watford 1-4 Man Utd
That's all, folks. United will line up as one of the finalists in the first FA Cup final in the new Wembley stadium. The scoreline was, perhaps, a little flattering but the result was never really in doubt.
1927: Alan Smith unselfishly moves the ball along in the Watford area, clearly trying to play in Wayne Rooney for his hat-trick but Watford clear the ball before it gets to him.
1925: Wayne Rooney sprints 40 yards as a part of a one-two with Ole Gunnar Solskjaer but then slices his shot wide.
1922: There really should have been a penalty there! Jordan Stewart's leaping lunge takes out Darren Fletcher. the Watford defender is nowhere near the ball but referee Howard Webb gives a corner.
1920: A massive shout out from the Watford fans, who feel Gabriel Heinze had his hands up in the air and connected with the ball. No penalty, though.
1918: GOAL Watford 1-4 Man Utd
And that really is all over now - if there had been any doubt at all. Kieran Richardson latches on to Alan Smith's precise pass and clips the ball over Richard Lee.
1915: Jay DeMerit is cautioned for wrestling Alan Smith to the ground. It looked like they were both at it, though. And there was no sign of a three-second pin down anywhere.
1913: Kieran Richardson comes on for Cristiano Ronaldo, while Watford replace Tamas Priskin with Marlon King. Jamaican international King has been out since the start of the season and receives a warm welcome from his fans.
1911: Michael Carrick goes into the referee's book for a tackle from behind on Tommy Smith. The Watfrod man is being bruised aalmost as much as Edwin van der Sar.
1910: Excellent defending from Gabriel Heinze as he nods away a cross which appeared destined to reach Damien Francis.
1908: Alan Smith twists and turns and lays the ball off to Wayne Rooney and it looks like the striker is about to complete his hat-trick. But no, Richard lee does well to save his close-range effort.
1906: Watford bring on Steve Kabba - he must be shattered, he's been warming up for 20 minutes. Well, I'd be tired, anyway. James Chambers makes way.
1904: Edwin van der Sar is taking a battering. A combination of Patrice Evra and Tamaas Priskin leave the keeper crumpled on the floor. I think he's had enough - and Tomasz Kuszczak is warming up. But the Dutchman gingerly picks himself up and punts a free-kick forward.
1902: GOAL Watford 1-3 Man Utd
United, who had been playing at half pace, suddenly motor through the gears and Alan Smith picks out an unmarked Wane Rooney, who slots in from 5 yards.
1900: Gavin Mahon latches on to a loose ball outside the box after Wes Brown clears poorly, but he sends his volleyed effort well wide.
1857: Patrice Evra is dazed and laying on the ground but no-one plays the ball out. United players surround Gavin Mahon - the last player to touch the ball before it went of play - to protest at Watford's lack of sportsmanship.
1854: Hameur Bouazza strips Gabriel Heinze but is then let down by a clumsy touch which allows Patrice Evra to come across and clear the danger.
1853: Poor from Tamas Priskin. He does well to shrug off his defender and then asks far too much of Hameur Bouazza with an overhit pass.
1851: Hameur Bouazza delivers a swirling cross from the left which curls goalwards and almost catches out Edwin van der Sar, who has to stretch to plam the ball away.
1849: A brutal-looking lunge from Wayne Rooney on Tommy Smith forces the referee to show the United man a yellow card. Incredibly, he complains strongly about it.
1846: Watford must be thinking of making a change as Steve Kabba begins to warm up on the touchline.
1845: A glorious chance goes begging as Hameur Bouazza steers a volley wide of the post from six yards out. It should have been all-square again.
1841: Watford get the second half started. And almost immediately Gabriel Heinze lunges into Tamas Priskin but is not penalised for the challenge.
1840: United's reserve keeper Tomasz Kuszczak just tried to trip Kieran Richardson as they walked to the bench. Richardson looked baffled.
BBC Sport's Caroline Cheese at Villa Park
1840: Watford have it all to do in the second half, but they are still in this game while they remain just one goal down.
1825: I thought it was all over after the first goal - and some of the United players did too. But there was a little bit of complacency and they conceded the equaliser. However, then they reacted again. And there are more goals in this for United.
BBC Sport pundit Alan Hansen.
1824: But the Hornets are not giving up - and so they shouldn't with only a goal in it. However, they will need to do better than the overhead kick which Clarke Carlisle balloons over the United bar.
1823: Watford live dangerously again, this time holding a high line but failing to catch Wayne Rooney offside. The England striker cuts inside but dinks his shot wide of the upright.
1821: A neat interchange of quick passing plays in Wayne Rooney and his shot brings a smart save from Richard Lee.
1819: Damien Francis agains gets his head to a free-kick without directing the ball accurately. However, with Rio Ferdinan off injured and United employing a makeshift defence, an aerial bombardment could prove fruitful.
1816: The decision is to replace Rio Ferdinand with Darren Fletcher, who slots in at right-back with Gabriel Heinze moving into the centre and Patrice Evra on the left.
1815: Sir Alex Ferguson and his assistant Carlos Queiroz are in conflab over what to do about Rio Ferdinand.
1814: United boss Sir Alex Ferguson has a word with Rio Ferdinand on the touchline. The England defender looks like he might be struggling with an injury.
1811: Damien Francis finds space in the United box but fails to make the most of a free header and does not trouble Edwin van der sar with his effort.
1809: Wayne Rooney attempts to prevent a long cross going out of play and ends up in the arms of a few Manchester United fans in the stand. He emerges from the mini mobbing with ruffled hair. Well, I think it's ruffled. It's hard to tell the difference, really.
1806: A heavy touch by a rampaging Cristiano Ronaldo allows Jay DeMerit to slide in with a superbly-timed challenge and nip the ball away from the Portuguese winger's toes.
1804: GOAL Watford 1-2 Man Utd
That didn't last long! Wayne Rooney breaks down the right and tries to slip a shot past Richard Lee at the near post - the ball deflects out to Cristiano Ronaldo, who does not miss chances from five yards.
1802: GOAL Watford 1-1 Man Utd
Watford take full adavantage of Edwin van der Sar's distraction as Hameur Bouazza volleys an acrobatic effort past the keeper, with the help of a deflection off Gabriel Heinze. Game on!
1800: What is it with Manchester United keepers' noses? Edwin van der Sar's is all red - but it is the result of a challenge from Clarke Carlisle, who catches him with his foot. United's physio comes on to stem the Dutchman's bleeding.
1758: Watford seem to have settled a little now and Hameur Bouazza curls a shot just outside the left-hand post. It is good to see Watford come into the game - everyone loves an underdog, don't they?
1754: The best form is defence is attack, some say. And Watford act on it to force a corner after Jay DeMerit's header is turned over the bar by a slightly disorientated Rio Ferdinand. No comedy own goal this time.
1753: Jordan Stewart does well to repel a wave of United attacks. He and his fellow defenders are in for a long night, by the look of things.
1751: The Cristiano Ronaldo showboat is already building up steam, he skips past three players and slides in Alan Smith, but the striker's control lets him down.
1748: In acres of space, Alan Smith blazes a shot high and wide. Watford look unsure how to deal with United's movement - and you have to say you fear for them at the moment. They appear to be overawed.
1747: Wayne Rooney darts towards the near post trying to meet a cross from the left but Richard Lee smothers the ball before he gets there.
1745: Watford boss Aidy Boothroyd sends a text from the stands - an S.O.S. perhaps?
1743: GOAL Watford 0-1 Man Utd
Sublime. Wayne Rooney cuts inside his marker and smashes a right-footed drive into the top corner. It's the worst possible start for Watford. Hugely unfancied before the game, could that be the end already for the Hornets?
1740: That sounds weird after seven years - hearing the crowd sing '...we're going to Wembley'. Personally, I think the Millenniumm Stadium is superb, but 'Cardiff' did sound odd when sung in the classic chant.
1738: Wayne Rooney takes a tumble after leaping with Jay DeMerit but United fail to manufacture anything from the resultant free-kick.
1736: Ryan Giggs and Alan Smith kick off as Manchester United get the weekend's first FA Cup semi-final under way.
1731: The players are lined up in the tunnel and there are a few nervous faces as they move off to enter the arena. They are welcomed by the bright yellow of the Watford fans, who look as though they outnumber United fans.
1730: The only way Watford can win is if Manchester United's players all have an off-day and Watford's are all at their top of their game.
BBC Sport pundit Alan Shearer
1725: The announcement of Marlon King's name is treated by the Watford fans as though it is the second coming.
BBC Sport's Caroline Cheese at Villa Park
1720: Watford fans are in far louder voice than Manchester United fans. However, it may be the only time Watford have the upper hand this evening.
BBC Sport's Caroline Cheese at Villa Park.
Marlon King is on the bench for Watford after a long injury lay-off and Paul Scholes returns for Manchester United after being suspended against Roma in midweek.
And Manchester United have named a full-strength side - resisting the temptation to rest the likes of Cristiano Ronaldo in order to boost their pursuit of the Premiership and the Champions League.
Who would you pick?
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