The 25-year-old Spaniard, a £37.1million capture from Chelsea, scored twice and set up Adnan Januzaj for his late strike as United cruised to a 4-0 Barclays Premier League win at St James' Park.
Manager Moyes said: "I think Juan Mata has played really well and I think he has made us better. He hasn't had the goals in the earlier games, but I really thought he played fine in the games.
"But recently he has started the get the goals and, more importantly, assists as well.
"Over the last few seasons in the Premier League, Juan Mata is one of the best assist-makers and he has always got himself a good tally of goals.
"We needed that and he is coming up with the goods now."
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