United has already won the Club World Cup and faces Tottenham in the final of the English League Cup on March 1. It leads the English Premier League and has reached the knockout stage of the UEFA Champions League -- both competitions in which it is the defending champion.
Nani, Darron Gibson, Cristiano Ronaldo and Danny Welbeck scored for United, which faces the winner of the Fulham-Swansea replay in the quarterfinals.
The play by Gibson, 21, and Welbeck, 18, reflect the new depth United has found to keep its bid for five trophies alive/
"I've been saying for some weeks with all the injuries, it's the squad that's been carrying us through difficult games and they proved it again," United manager Alex Ferguson said. "I made some changes and it worked out well."
The marque match of the fifth round featured Everton against Aston Villa in a battle of American goalies. Tim Howard came out on top as Everton put three goals past Brad Friedel in a 3-1 win at Goodison Park.
Chelsea, a 3-1 winner over Watford, is the only other team definitely into the quarterfinals.
FA CUP, QUARTERFINAL DRAW
Blackburn Rovers or Coventry City (II) vs. Chelsea
Swansea City (II) or Fulham vs. Manchester United
Cardiff City (II) or Arsenal or Burnley (II) vs. Sheffield United (II) or Hull City
Everton vs West Ham United or Middlesbrough
(Dates: March 7 or 8)