Juventus coach Zaccheroni cannot explain stunning Siena fight-back
Despite leading 3-0 after 10 minutes, Juve were pegged back 3-3 by the minnows.
"I have never seen a game like it," said Zaccheroni. "We had the right approach to the game and immediately scored three goals with good football and fast moves.
"Then we conceded one because of our mistake and the reaction that followed absolutely needs to be different.
"We are a great side when we are in the game, but the moment we lose focus absolutely anything can happen."