Mata struck in the first-half as United beat the champions 4-1.
He told MUTV: "I think we needed something like this. We won the Cup game in the week, but we needed something in the Premier League and we showed it.
"We scored four goals, four different goals."
Mata added: "I can't remember us playing so well in the first-half since I've been here.
"We're always working on corners. We know we have strong people who can score in the box."
On United's second-half fade-out, Mata added: "You have to keep going. They scored the first one and if they scored a second quick one we'd be nervous, so we had to take back control and we did."