Mata created two goals as United put behind them the misery of defeats to Arsenal and Manchester City in the new year, as well as a dour draw with Wolves, to thrash Norwich 4-0 in the Premier League.
Marcus Rashford scored twice on his 200th United appearance before further efforts from Anthony Martial and Mason Greenwood in a one-sided encounter at Old Trafford.
"It was a good performance and a performance that we needed," said Mata, who crossed for Rashford's volleyed opener and a Martial header.
"It is a performance we can look at and see how we can play, and make sure we play like that on a more consistent basis", said the Spaniard.