Chelsea's incredible record in the FA Cup was extended thanks to a wonderful finish from Demba Ba that helped Rafa Benitez's side claim a crucial win that gives them the opportunity to win the trophy for the fourth time in five years.
After losing to Southampton in the league on Saturday it was vitally important that Chelsea bounced back against United. A wonderful save from Petr Cech to deny Javier Hernandez made sure of the clean sheet after Ba had volleyed his side ahead with a sublime finish.
Chelsea's victory means they will now meet Manchester City for a place in the FA Cup final where they will face either Wigan or Millwall.
While Chelsea had suffered a shock defeat just days ago, Manchester United had rested a number of players for their comfortable 1-0 win over Sunderland and where able to field a strong side despite the absence of Wayne Rooney and Robin van Persie.
Rooney missed the game with a groin injury while Van Persie was left on the bench as Sir Alex Ferguson preferred to start with Hernandez and Danny Welbeck.
There were few opportunities for the two forwards in the first half with the biggest moment coming when Ashley Cole attempted to keep up with Welbeck and pulled up holding his hamstring. Ryan Betrand came on to replace the England defender less than half an hour into the game.
It took until 32 minutes before we had the first shot of the game and it came after good work from Eden Hazard who played in Ba who hammered a hard low shot, which David de Gea did well to block with his boot.
Nani and David Luiz traded long distance efforts which failed to trouble either keeper before Hernandez also attempted his luck from all of 30 yards. His strike swerved at the last second and Cech, who had dive the wrong way, was forced to save with his feet.
There was a penalty appeal from Nani who claimed he was pulled back by Bertrand but referee Phil Dowd waved away the claims.
After a forgettable first half it did not take long before Chelsea took the lead as Juan Mata picked out a beautifully lofted ball which Ba somehow managed to stretch out a leg and volley the ball past a helpless De Gea.
United managed to respond and Cech was then forced to produce one of the saves of the season after Hernandez's diving header looked destined for the far corner. The striker guided the header back past the Czech keeper who somehow managed to get a string hand onto the effort to tip it over the bar.
As United pushed forward in the search of an equaliser, Chelsea had a number of opportunities to put the tie to bed but they were guilty of wasting numerous chances.
Eden Hazard had the best opportunity as he burst into the penalty area following a mistake from Michael Carrick but his shot went inches wide.
There was a late chance for Van Persie who was picked out by Patrice Evra but the Dutch striker's volley ballooned well over the bar.
Chelsea will now travel to Wembley where they will be hoping to make yet another FA Cup Final as they bid to win the competition for an eighth time.
"I am really pleased because the players were doing a great job. Manchester United are a very good team and we did really well," said Benitez. "We have good balance between the defence and midfielders. Physically you could see one or two challenges we could not cope but with the ball we were much better.
"It was a fantastic goal by Demba Ba but everyone's performance was really pleasing. Petr Cech made some good saves but at the end of the day we deserved to win."