De Gea was the match saver as Emanuele Giaccherini would have put the Black Cats into a 2-0 lead with United in a vulnerable position.
"David's save was one of the best I have ever seen," said the United manager.
"It was an incredible save and I said it straight away to the bench.
"It was amazing, it really was. Right up there as one of the best I have ever seen and that was a turning point."
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