"The first half performance you would have to say was superb, absolutely marvellous," Fergie told Sky Sports.
"The second half was disappointing. I think they just took their foot off the pedal, relaxed and went down a gear.
"Against Everton last Saturday it was a different issue all together.
"Tonight they were just far too relaxed. I think they enjoyed themselves too much.
"But we played very well in the first half."