The Dutch goalkeeper's fitness had been a concern, because he has been troubled with a groin problem.
"Edwin showed why he has 120 caps. His experience is vital.
"He made one incredible save in the second half and is a great goalkeeper.
"We rode our luck in the first 15 minutes of the second half. You get those breaks sometimes - and we did today."
United's celebrations were tempered as defender Nemanja Vidic was forced to come off with a knee injury in the 33rd minute.
He will have a scan tomorrow, and Ferguson said: "I pray it is not serious, because he is such an integral part of our team.
"We think it might just be a nerve injury but we can't be sure at this moment."