The Italian said: "I have never seen an unbeatable team. Chelsea is not unbeatable but we are doing well.
"I am not surprised by our start to this season. I had one month before the start of the season to know the players, their mental attitude and their quality.
"I know the rivalry between the two teams and how important this match is for the fans. We have to pay attention to this and we want to win.
"We have to pay attention to this because they can cause us difficulties in the game."
But Ancelotti insists his side are full of confidence ahead of the game.
"We are in a very good condition and have a very good feeling about our play. We have the possibility to win this important match," he said.
"I said last week that this is a very important moment of the season and we have started very well with victory over Stoke and Porto and we want to continue this.
"Tottenham will play two strikers that we will have to control. We know the quality of Peter Crouch, Lennon and Defoe. They can be dangerous because they are very quick. We don't leave the possibility for them to counter-attack against us.
"We want to start at the top of the league and maintain this position and if possible, improve the distance between us and the second placed team."