The England star dominated the midfield battle as West Ham ran out 1-0 winners at Goodison Park.
Speaking to reporters, Moyes said: "It would be very hard to say how good he was. He was excellent.
"For me he was head and shoulders above everybody on the pitch today, he passed it, took control, wanted the ball, received the ball and tried to create opportunities.
"He did the dirty bits in the game when he had to do so but also had a great air of control and poise when he was on the ball. So I don't know if I could not speak highly enough about Declan today but I would be saying that for most of the season.
"There have been games when I think he could have stepped up a little bit more. But there has been big improvement in Declan and obviously, that's good for us."
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