City beat the Blues 1-0 at Stamford Bridge on Saturday to return to the League summit.
That defeat has left Chelsea six points behind Pep Guardiola’s side and Manchester United in the title race.
But they trailed Manchester City by eight points at the same stage 12 months ago before going on to claim the trophy.
And Willian said: “They (the Manchester clubs) have started very well, but in football it is not important how you start, it’s important how you finish.
“Last season we didn’t start too well but then we arrived there (in first). We have to always be ready for everything.
“Chelsea always try to bring players with quality and the ones that have arrived, have quality to play here. The squad is still strong, the team is still strong and we have to push until the end of the season.”