"It was fantastic, a marvellous performance from Dimitar again," Fergie said after the match at Old Trafford.
"He's bringing that composure to the final third of the field.
"Dimitar showed some fantastic pieces of football. I also think the other players are beginning to understand what type of player he is.
"You always feel he can produce a pass that means something and his weight of pass on three or four occasions was superb. He has got five goals for us already and that is a terrific contribution.
"I was really pleased with our performance. It was a really bad night for Celtic to get us and a good night for us."