Romelu Lukaku scored a brace in his first Premier League match for United at Old Trafford, followed by goals from Anthony Martial and Paul Pogba.
“It was a joy to have a game like this one, we needed it after failing to win the first title of the season in Skopje,” Mata wrote in his blog, referring to their Uefa Super Cup loss to Real Madrid.
“I hope we can have many more games like that, even better if there are 37. Obviously we know it will be complicated, because this is the toughest league in the world and every single game is a difficult test.
“These are the first three points and they will be even more important at the end of the season.
“The year is going to be especially exciting because we are back in the Champions League, and we don’t forget the two cups, of course.
“That’s a lot of things to fight for, as usual, so we have to go little by little, stay together and work tirelessly. That’s how you get to your long-term goals.”