City powered into a double-digit point lead at the top of the table after goals from David Silva and Nicolas Otamendi gave them a 2-1 win over United at Old Trafford last weekend, with Marcus Rashford scoring a consolation goal for the home side on the stroke of half-time.
Pep Guardiola's side went on to beat Swansea in midweek to extend their winning run in the league to a record 15 matches, but Mata said United were only focusing on themselves and not on what City were doing.
The Spaniard suggested that the Red Devils would have to keep chalking up wins and stay within touching distance of City in the run-in and hope for the best.
"In any other different season, we probably would be top of the Premier League with this amount of points (38)," Mata was quoted as saying by Goal after the 1-0 win over Bournemouth.
"But we need to focus on ourselves. Obviously City are doing very well, that's why they are first in the table.
"But we need to focus on us and how well we are doing. We also need to be learning from the games we didn't win and then carry on through this difficult Christmas period.
"Hopefully, come the end of the season, we'll be fighting for the title."
Mata said United had a lot to look forward to in the second half of the season despite the obvious disappointment of losing the Manchester derby.
"The most important thing is we are doing all right as a team," he stated.
"I think we are doing well in the Premier League, even though we are not in the position we'd like to be in.
"We have a lot of points in this early stage of December and we've qualified first in the group in the Champions League, plus there are the two other cups."