A Jonathan David penalty saw the hosts shock the defending title holders.
Ancelotti later said: “The sadness comes from the team's impression, that it wasn't a good game. It's sport and you can lose, but we didn't give a good account of ourselves. That's what worries me the most, but we have all the resources to learn from this defeat and do better. We have to put things right fast because we have another game on Saturday.
“I'm very honest. The criticism for today's game is fair, correct, and we have to accept it because that's the way it is. We didn't perform well in this game. When we lost the derby last year it was a huge wake-up call and hopefully, this defeat can also be a huge wake-up call.
“Fortunately it hasn't happened many times recently when the opposition plays better than you and deserves to win. We struggled to get into the game and with the battles. We might've drawn the game and we had chances at the end, but we didn't deserve to win. We have to learn and know what we have to improve, like the last time we lost. I don't think it's too difficult.
“It's difficult to evaluate today's game. We did everything wrong: with the ball, in transition, intensity, we lost the duels. We have to look at things with a calm mind and not drop everything, but we have to improve. We struggled to generate and create. Possession was slow and we lacked ideas. We have forwards who need to play more directly than usual and if you play slowly it's a problem.”
He added: “Just talking about it is not enough to fix it. There's a dynamic that needs to be improved. It's not enough to talk about it. The team was improving and this match is a setback. We have to keep fighting, battling and improving.”