Valencia have defied critics this season with an impressive run of results under coach Unai Emery.
But midfielder Mata says: "We're aware we have to be realistic.
"We're in a good situation with a great start of the season, but there's still another half of the championship to go and it's always difficult to keep that consistency.
"It's still too early to talk about winning La Liga. The target of the team is trying to win at the end of the season."