After victory over Chelsea, De Jong offered some insight into Mancini's game plan - for the season as well as this particular occasion.
He said: "He has come from a country where defence is No 1 and he has brought that mentality with him.
"The main focus for him is to get the defence right because he knows we have enough quality to score goals - especially at home. That's what he preaches. That's always his message - don't concede. It will take time but this was an important step towards the future.
"I think it is the mindset of every player in the team that has changed. The belief is there. He spends more time on the training pitch with the defenders to get them to realise that a clean sheet is holy. This result shows that Chelsea are not robots."