Watford United 1 Man United 4:A goal in either half by England striker Wayne Rooney ensured Manchester United will face either Chelsea or Blackburn Rovers in the FA Cup final at Wemblet, but they didn't have it all their own way at Villa Park as Watford refused to roll over for the home side.

The signs looked ominous early on for Aidy Boothroyd's side as United's began in the manner which saw them put seven past Roma's defence on Tuesday evening.

Rooney opened the scoring emphatically in the seventh minute when he blasted a right foot shot high into the net from the edge of the box.

Watford struck back though, through Hameur Bouazza in the 26th minute. Gavin Mahon's long throw-in was only half-cleared by Rio Ferdinand, allowing Tommy Smith to hook the ball back into the danger zone, where Bouazza's acrobatic volley from eight yards deflected off Gabriel Heinze and went in off the underside of the bar.

However, Watford's delight lasted only two minutes, with United regaining their lead in the 28th minute.

Alan Smith released Rooney on the right, with the England striker outpacing Carlisle before slipping the ball inside to give Ronaldo a simple finish from four yards for his 21st goal of the season.

At the other end Edwin Van der Sar did not look confident and the Dutchman's parry from Mahon's 30-yard effort on the half-hour mark was decidedly shaky.

United's defence was not shining brightly either and they were relieved to see the unmarked Damien Francis head Jordan Stewart's right-wing corner wide 10 minutes before half-time.

The Red Devils suffered blow, of sorts, in the 40th minute when Ferdinand, who appeared to be suffering from a groin injury, decided he could not continue, and he was replaced by Darren Fletcher.

Fletcher slotted in at right-back, with Evra switching to the left and Heinze playing alongside Brown in the centre.

Watford began the second half with a renewed vigour but United were ruthless and when the did hit the target for the first time in the second period they scored, thanks again to Rooney, this time from close range.

United's safe passage into their 18th FA Cup final was ensured when Kieran Richardson, on for Ronaldo, deflty chipped the ball over Watford goalkeeper Richard Lee after being put through with a neat ball from Smith.