Sarri left Napoli last summer for the Blues in an acrimonious departure.
“Of course I was a Chelsea fan yesterday, I was supporting an Italian first of all," De Laurentiis told reporters.
“In fact [I was supporting] two. In addition to Sarri, there was also Jorginho.
“I immediately congratulated Sarri, also because taking him to Napoli was my decision, which at the time was opposed by everyone.
“The ultras wrote that I was wrong on all the walls of the city, but I'm used to it.
“I remember I was criticised when I gave Quagliarella to Juve and replaced him with Cavani, yet today everyone would take him back."