Chelsea saw off a fightback from Tottenham to progress to the semis while a 75th minute penalty by Cristiano Ronaldo was enough to ensure Man Utd kept their treble hopes alive.
Chelsea will take on Blackburn Rovers at Old Trafford on April 15th while Manchester United will play Watford on the 14th at Villa Park.
FA Cup semi-finals
April 14
Watford v Manchester United, Villa Park (1630 GMT)
April 15
Blackburn v Chelsea, Old Trafford (1500 GMT)