But Sir Alex Ferguson's men rallied to level via Rafael's brilliant curling effort five minutes after the opener before Robin van Persie won the game with a late penalty but the Brazilian defender knows it was a below-par showing on an emotional day for both clubs.
"Both clubs have a great history and we had to respect that, then we got the three points, which is so good for us," said Rafael.
"It wasn't a great performance from us but in the last five years we haven't won here so we're very pleased.
"Robin van Persie had to wait a long time to take his penalty. It might make some people anxious but he is a top player and he found the net."