With all the experience of the Scottish tactician, he admitted the noise and atmosphere unnerved him and his players although they did settle to record a come-from-behind 3-2 win over AC Milan in the Round of 16.
"The one thing that's so amazing is that for the first 15 minutes I was feeling in shock, really in shock, because the atmosphere was unbelievable," said Ferguson.
"That, coupled with the noise when they scored, it certainly unnerved me, and it unnerved my players.
"No matter how much experience you've got, you get into that cauldron of noise, and the response it had from the Milan players, and you're in there.
"So to get through that really did take a lot of courage. Our back four had to compose themselves, that was the most important thing.
"After that they settled, got very composed and got back to their normal game, and the result was different because of that.
â€œThe San Siro has been a bit of a hoodoo for us, but you've got to remember that AC Milan have a fantastic history.
"So it's no shame to not win there because they've always had a fantastic team, and the atmosphere there was absolutely fantastic. It was a great atmosphere."