Antonio Conte admits that he was not sure whether Chelsea would be able to adapt to playing in a 3-4-3 formation.
The Blues boss said he had to wait for the right moment to make the change which has seen his side win 11 consecutive games in the Premier League to go seven points clear at the top of the table.
Having seen his team lose twice in three games in September - 2-1 at home to Liverpool and 3-0 at Arsenal - Conte decided to switch to his favoured back three.
"In the history of Chelsea, this never happened, no?" he said. "To change it totally, this situation, is not easy - you must go slowly, slowly.
"In my mind, and also before the games against Liverpool, there was the will to change, but I waited until the right moment.
"Before the game against Liverpool, I understood our formation wasn't good to face Liverpool, tactically, and we paid for this
"You always hope not to make great changes to the team. I have players that had only played with four [at the back]."
Conte also believes the defeats to Liverpool and Arsenal resulted in a change of attitude around Chelsea which has inspired their run to the top.
"After the defeat against Liverpool, and also against Arsenal, it changed something in me, in the players, in the club," he said.
"We understood the way to go and have a different season, compared to last season.
"It was different. For this reason, we found the right solution, formation, but also to improve the quality of the work in all aspects.
"After these two bad games, we changed a lot.
"Usually when I don't win it's very difficult to sleep, but now I'm sleeping!
"After 11 wins, we have a positive pressure that we want to continue."