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  The Abbey Stadium delivered a thunderous roar as referee Chris Foy sounded his final whistle to confirm Cambridge - lying 12th in their division and 76 places below their Premier League opponents in the football pyramid  - had secured a money-spinning replay at Old Trafford.
  And even though United had the better chances, with Cambridge keeper Chris Dunn saving brilliantly from Radamel Falcao and Angel Di Maria and substitute Robin van Persie off target - no-one could begrudge them a second crack at Louis van Gaal's side.
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  Cambridge have almost been rebuilt as a club, returning to the Football League this season after a nine-year absence, and this performance was testimony to all that work as they more than matched the Red Devils until tired legs inevitably took their toll late on.
  And now that process will continue in "The Theatre Of Dreams" as they survived the meeting with a visiting side lacking the spark of captain Wayne Rooney, and failing to create any serious openings until the second half.
  Van Gaal, whose side battled thought a third-round meeting with Yeovil Town, will have been bitterly disappointed with his team's lacklustre display - even though they are still overwhelming favourites to reach the fifth round.
  United, who rested Rooney and Juan Mata, lacked creativity during a laboured first 45 minutes in which they were more than matched by Richard Money's underdogs.
  Money made no secret of his plan to unsettle the Premier League side, with seven players crammed into the six-yard area in an attempt to make life difficult for goalkeeper David de Gea with sheer weight of numbers.
  And with Phil Jones a symbol of that uncertainty, the obvious ploy almost worked on the half-hour.
  Manchester United failed to clear a corner and the ball was smuggled off the line before a header from Cambridge defender Josh Coulson landed on the roof of the net.
  Falcao's struggle for goals has been the focus of much attention but it was hard not to sympathise with the Colombian as he struggled in the face of poor service, which even when it did arrive was nearly always too pedestrian.
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  He finally got his chance just after the hour, when Michael Carrick delivered a forward pass of quality. Falcao applied a powerful finish but drew an equally strong one-handed save from Dunn.
  Van Gaal had seen enough and made changes, sending on Van Persie and Ander Herrera for James Wilson and the ineffective Marouane Fellaini.
  And Van Persie almost answered the call right away when he ran on to Di Maria's astute pass on the angle but directed his first-time effort over the top.
  Cambridge had given so much that it was inevitable fatigue would play a part in the closing minutes - and so it proved - but goalkeeper Dunn was once more the hero, punching clear crucially before recovering to block Di Maria's goalbound effort, surrounded by players in the area,
  It was the final moment of concern - leaving Cambridge's fans to celebrate wildly and savour the prospect of a trip to Old Trafford.
  Cambridge boss Richard Money:
  "We've said in the dressing room you're going to Old Trafford. Who cares what happens? Just go and enjoy it, soak it in. Whatever happens, happens.
  "(It is) difficult to put into words just how proud we are. When you get back in the dressing room and recover, you just suddenly start to think about what it means to so many people.
  "This club has been in the doldrums for 10 years, out of the Football League, and suddenly here we are taking everybody back to Old Trafford. It's incredible."
  Match ends, Cambridge United 0, Manchester United 0.
  Second Half ends, Cambridge United 0, Manchester United 0.
  Foul by Falcao (Manchester United).
  Josh Coulson (Cambridge United) wins a free kick in the defensive half.
  Attempt saved. Ángel Di María (Manchester United) left footed shot from outside the box is saved in the centre of the goal.
  Attempt blocked. Adnan Januzaj (Manchester United) right footed shot from the left side of the box is blocked. Assisted by Luke Shaw.
  Foul by Michael Carrick (Manchester United).
  Cameron McGeehan (Cambridge United) wins a free kick in the attacking half.
  Attempt missed. Falcao (Manchester United) header from the centre of the box is close, but misses the top right corner. Assisted by Ángel Di María with a cross.
  Substitution, Manchester United. Luke Shaw replaces Daley Blind.
  Foul by Adnan Januzaj (Manchester United).
  Tom Champion (Cambridge United) wins a free kick on the right wing.
  Corner,  Cambridge United. Conceded by Phil Jones.
  Foul by Robin van Persie (Manchester United).
  Michael Nelson (Cambridge United) wins a free kick in the defensive half.
  Corner,  Manchester United. Conceded by Michael Nelson.
  Substitution, Cambridge United. Luke Chadwick replaces Liam Hughes.
  Dangerous play by Ángel Di María (Manchester United).
  Tom Champion (Cambridge United) wins a free kick in the defensive half.
  Corner,  Manchester United. Conceded by Greg Taylor.
  Attempt missed. Robin van Persie (Manchester United) left footed shot from the left side of the six yard box is too high. Assisted by Ángel Di María with a through ball.
  Attempt missed. Phil Jones (Manchester United) right footed shot from outside the box misses to the right. Assisted by Ander Herrera.
  Cameron McGeehan (Cambridge United) is shown the yellow card for a bad foul.
  Ángel Di María (Manchester United) wins a free kick in the attacking half.
  Foul by Cameron McGeehan (Cambridge United).
  Substitution, Manchester United. Ander Herrera replaces Marouane Fellaini.
  Substitution, Manchester United. Robin van Persie replaces James Wilson.
  Offside, Manchester United. Daley Blind tries a through ball, but Falcao is caught offside.
  James Wilson (Manchester United) is shown the yellow card for a bad foul.
  Foul by James Wilson (Manchester United).
  Tom Elliott (Cambridge United) wins a free kick in the defensive half.
  Attempt blocked. Adnan Januzaj (Manchester United) left footed shot from outside the box is blocked. Assisted by Ángel Di María.
  Corner,  Manchester United. Conceded by Chris Dunn.
  Attempt saved. Falcao (Manchester United) right footed shot from the centre of the box is saved in the centre of the goal. Assisted by Michael Carrick with a through ball.
  Adnan Januzaj (Manchester United) wins a free kick on the left wing.
  Foul by Liam Hughes (Cambridge United).
  Corner,  Manchester United. Conceded by Richard Tait.
  Substitution, Cambridge United. Harrison Dunk replaces Sullay Kaikai.
  Offside, Cambridge United. Cameron McGeehan tries a through ball, but Michael Nelson is caught offside.
  Foul by Marcos Rojo (Manchester United).
target: League Two side Cambridge United defied the odds to hold Manchester United and earn a richly deserved FA Cup fourth-round replay.