The Spaniard produced a brilliant stop to deny Emanuele Giaccherini at the Stadium of Light, before the Red Devils came from behind to claim victory at the Stadium of Light.
And Moyes believes that the 22-year-old has now settled in the Premier League following a shaky start to his career in England.
“It [the save] is one of the best I have ever seen,” said Moyes.
“It was incredible. I said it on the bench right away, what a save it was.
“That was a turning point. I don’t think we deserved to be losing but had we gone 2-0 down, then it would have been a mountain to climb.
“I think he has definitely established himself now. It was brave for Sir Alex to bring him in and there probably were a few seasons when it might have been a bit rocky.
“Hopefully David will feel the benefit of that in the years to come.”
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