Fábio da Silva put the home side ahead after 28 minutes when he pounced on a loose ball after Manuel Almunia could only parry Javier Hernández’s effort.
Then Wayne Rooney struck in the second half and United were on their way, but they needed help from Man Of The Match van der Sar.
“Edwin was fantastic,” said Ferguson.
“He made a mistake last week [at Liverpool] and dropped a goal but he’s more than repaid us in full today.
“It’s not just his ability as a goalkeeper, it’s his calmness he brings to everyone – that’s a vital ingredient he has.”
Arsène Wenger’s side were unable to find a way past the Dutchman but Ferguson was looking for a response from his side after consecutive league defeats, and he believes he got it.
“It was a massive game for both clubs in a fixture that is always going to be intense,” he continued.
“In fairness Arsenal played their part in the game but I thought in the second half in particular we played well. It was always going to be a tough tie so we are very pleased.
“They did have a few good chances and Edwin van der Sar has made some spectacular saves, but we missed a few very good opportunities ourselves so at the end of the day there wasn’t too much in it.
“Arsenal probably had more of the chances if I’m being fair, but we were always a threat, especially after the break.”