"I would have trouble explaining how we lost that in Spanish - in English I find it almost impossible," he said.
"We dominated the game, were in control and had plenty of attacks. Sometimes football is all about luck. When you have so much of the play and make chances without scoring, you must be careful against a team as good as United.
"United have a great defence and a fine goalkeeper. He stopped one from Peter Crouch at the end everyone felt was going in. But although we had so much of the game, we did not make too many chances.
"The decision to disallow Craig Bellamy's effort in the first half for offside was right. It just was not our day."
He added: "United are really close to the title now. Chelsea are a good team, but they cannot make mistakes now because United will continue to win.
"As for us, we are down now, but we will train hard and be ready for Barcelona on Tuesday."