Moyes, talking ahead of his first return to Everton on Sunday since moving to Old Trafford, believes the Spaniard has instantly proved his worth following his £37.1million January move from Chelsea.
Mata has scored three goals in 11 Premier League appearances – all coming in his last two outings - and his creativity has helped a team in transition under Moyes.
"I think it's gone a little bit amiss but Mata has been terrific in his play," said the Scot.
"One thing I will say is it's been missed how well Mata has done.
"He's started to assist goals and score goals and has struck up an understanding with Wayne (Rooney) and with who he's played with.
"Juan has been a little bit overlooked.
"I could nearly say you (the media) don't want to talk about anything so positive, but he's been really good."
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