SIR Bobby Robson admitted the sending off of Andy O'Brien cost United the game as they went down 5-0 against high-flying Chelsea at Stamford Bridge on Sunday.

Chelsea were 2-0 in front courtesy of goals from Glen Johnson and Hernan Crespo when O'Brien's tug on Crespo saw referee Paul Durkin point to the spot and issue a straight red card.

TV replays later showed the foul had taken place outside of the box, but that mattered little when Frank Lampard despatched the spot kick and second half goals from Damien Duff and Eidur Gudjohnsen completed the rout.

"It was a double blow for us, because what the referee deemed as a foul took place outside of the box, and the sending off rubbed salt into the wound," said Sir Bobby.

"We're 2-0 down at that stage, and once the penalty goes in it's 3-0 at half time and it's game over then. I said to the players at half time I didn't expect us to go and win the game, but I wanted some heart and some passion for the shirt and for long spells I got that.

"We did well in patches, but Shay has sent a poor clearance straight to Duff for the fourth, and I don't know where my centre halves were for the fifth goal. I think they must have been sitting next to me.

"5-0 is not a result I like, it sounds like a hammering and what we have to do now is forget all about it and get on with things."

Sir Bobby's cause was not helped by the fact that Alan Shearer was ruled out after going down with the flu before the game, though he still felt his team had a chance of getting something from the game against the big-spending Blues.

"They have done well this season, but they can't win every game and I just thought that this would be the game they lost. I really did. We were flying after the win in Basle, and they were full of confidence too after beating Lazio but I felt we could do it," he added.

"Losing Alan was a blow for us, it became clear at lunchtime that he wasn't going to be fit to play a part. I went for Hugo as an extra midfielder to try and combat the threat of Makelele, and for a while it worked.

"We started brightly, but at the end of the day it just didn't go for us and as I said earlier we have to take it on the chin, forget about it and get ready for the next game."