The two are the undisputed creative forces in the Chelsea team, with the Blues relying on them for creativity, assists and goals.
Willian is in great form in recent weeks, while Hazard is quietly having another very impressive season.
"He's [Hazard] a very good guy, and we have a great relationship off the pitch," Willian said to Chelsea FC Magazine about their friendship.
"I think, when you have a great relationship off the pitch, things come easily when you are on it together. With him, it's easy to play.
"It feels good when we combine. I feel happy. He has a lot of quality, he's an amazing player."