The Old Trafford side were rattled and Rio Ferdinand kicked the ball into the crowd and hit a spectator when the referee did not play an advantage with United's frustration boiling to the surface.

BBC: SPORT | Football | Premiership | Man Utd 4-1 Blackburn

"The Celtic fans jumped up and down and screamed and shouted as they do and the referee gives it and books my player as well when the ball was already out before the player hit the deck, so I just think the referee has got to be a bit stronger, " said Butcher.

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Centre-back Koscielny was left off balance on the edge of the area and tried to pull his foot out of the challenge but the winger hit the ground after minimal contact and the referee was quick to point to the spot.

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At the other end, United were perhaps unfairly denied a penalty by referee Andre Marriner when Hernandez's shot hit the outstretched arm of a sliding Gary Cahill.

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It was clear there was going to be no stopping Khan and after more punishment, Kristjansen hit the deck for the third time in the round and the referee called a halt to the contest.

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Tam Scobbie glanced a header wide from a corner when he ought to have hit the target and Falkirk paid for that miss after 29 minutes after referee Willie Collum ruled that Kevin McBride had pushed Aiden McGeady.

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