Pep Guardiola's in-form side make the short journey to Old Trafford on Sunday, when Jose Mourinho's second-place Reds will attempt to end their rivals' unbeaten Premier League run.
Suspended Paul Pogba has admitted United "need to win" given the eight-point cushion City have already built and Mata too is desperate to secure derby victory.
"We are doing what we have to do," the Spain international said ahead of this weekend's "special game".
"We would love to be first in the table right now but I think we are doing lots of good things.
"Now, especially on Sunday and during Christmas time, which we all know how difficult it is to win every single game, we need to keep that pace if we want to be in a position to challenge for the title at the end of the season. Hopefully we can do it."
United certainly boast the strength in depth to maintain their title challenge heading into a testing festive period.
City have had to dig deep to eke out victory in recent matches and Mourinho's men are ready to capitalise on any drop off.
"We need to look at the bigger picture," the attacking midfielder said. "We have just started December and December is a crucial month with a lot of games.
"If we arrive in a position where we want to be in February or March then we can think about 'we won on Saturday and they won on Sunday'.
"It's not the best feeling but we think about the bigger picture and for us we have to keep up the pace and keep winning and winning.
"It's very difficult, especially in the Premier League.
"When you play Watford, Stoke, West Ham away or whatever it's very difficult to win every single game and we need to be ready if they drop points."
Guardiola's City have been priced as short as 1-16 to lift the Premier League while United are 10-1 with bookmakers and some pundits have already given City the title.
"Most of (the pundits) have played football and they know how football can change," Mata said.
"I remember a few seasons ago when United were ahead of City and then they won by goals. It's a crazy league and it's too early to think that it's finished.
"From City they will tell you the same."
Mata was not getting involved in talk of compatriot David Silva potentially missing Sunday through injury, saying with a laugh "we know about that" when asked about potential City mind games.
However, from United's end there is no disguising the absence of Paul Pogba through suspension and the impact that will have.
"Yeah, big miss," Mata added after the 2-1 defeat of CSKA Moscow in the Champions League. "He's a fantastic player.
"He did a fantastic assist (on Tuesday). He's a very complete midfielder, he can do all things. He will be a big miss but another player will play and try his best.
"I think we have a good squad and have good players to replace any other player. Hopefully we can win for him."