UPDATE 1-Soccer-Man Utd beat Watford to reach 18th FA Cup final

(Updating with details)

LONDON, April 14 (Reuters) - Manchester United booked their place in the first FA Cup final at the rebuilt Wembley Stadium when they beat Watford 4-1 in an entertaining semi-final at Villa Park on Saturday.

Two goals from Wayne Rooney and one each for Cristiano Ronaldo and Kieran Richardson secured United's path into the May 19 final, the first at Wembley since 2000, when they will face either Chelsea or Blackburn Rovers, who meet at Old Trafford on Sunday.

United, who will be appearing in a record 18th final, have won the competition a record 11 times and have now reached their eighth FA Cup final under manager Alex Ferguson.

The victory keeps them on course to win three trophies this season -- the Premier League title, the FA Cup and the Champions League -- and repeat the treble they achieved in 1999.

BLISTERING SHOT

Rooney put United ahead after seven minutes when he cut inside his marker, made space for himself and smashed home a blistering right-foot shot that left goalkeeper Richard Lee -- a diehard United fan as a child -- diving in despair.

Although United were largely in control, Watford replied with a surprising equaliser after 26 minutes when Hameur Bouazza latched on to a loose ball and volleyed it past van der Sar.