The Red Devils are the early leaders in England's top flight after following a 4-0 win over West Ham United on the opening weekend of the season with a 4-0 victory at Swansea City on Saturday afternoon.
Mata has said that United "have reasons to be happy with the confidence and determination", but claims that his teammates have their feet firmly on the ground.
"In terms of football, the week ends with a very good feeling again, following another convincing victory, although perhaps the score was too high," Mata wrote in his official blog.
"One thing is for sure, we have reasons to be happy with the confidence and determination that we are showing on the pitch, but we also know that this is just the beginning.
"The next weekend we have a new opportunity to keep gaining momentum, this time against Leicester, always a tough opponent. It would be great to take the first international break of the season with nine points out of nine."
Mata has started both of United's Premier League matches this season.