Willian is thrilled to be playing under Maurizio Sarri after coming close to leaving Stamford Bridge following a row with former Chelsea boss Antonio Conte.
Willian made no secret of the breakdown in his relationship with Conte, previously saying there was "no chance" he would have stayed at the club had the Italian not left.
Willian has featured in all five Premier League games under Sarri and is set to face PAOK with Eden Hazard rested after his hat-trick against Cardiff City on Saturday.
"I am very happy. Always I was happy at Chelsea," Willian said to reporters. "I don't want to talk about the past.
"I am happy with the new manager and profile of football. I think we have a great team atmosphere and we can do everything to win titles.
"I am very proud to stay and be a Chelsea player. It is an honour to play at this club. I am very happy at Chelsea.
"Everyone knows what happened in the last window. My mind was always to play at Chelsea, now with Sarri we have a different way to play.
"He wants us to play. You can tell in the game, we play with more possession and have more fun and win five games in a row. We have to continue in the same way."