The winger has hailed the manager as "one of the best coaches in the world", and was delighted to finally sign for the west Londoners in the summer after long-standing interest
The 25-year-old was signed for a reported £30 million from Anzhi Makhachkala, where he had only played for seven months having joined from Shakhtar Donetsk the previous January.
And Willian feels settled at Stamford Bridge, stating that manager Mourinho was having a positive influence on his career.
"My first impressions of Mourinho were really positive," he told Fifa's official website.
"He is one of the best coaches in the world and he said that he was delighted that I had come to Chelsea, and that he liked the way I play. We talk a lot, and it’s really helping me. I’m learning so much.
"At Shakhtar I was already established and was comfortable with the way the team played," he continued. "Here I have to push myself twice as hard, because there are so many great players around me.
"But I like the pace of the game in England, and the tackling. I’m getting better every day and I know that I can’t relax: if I play well in one game, I have to do even better the next time out."
Chelsea were reported to have made enquiries about the player in every transfer window since 2011 before getting their man, and Willian admitted he had taken a keen interest in the club's form since then.
"I kept an eye on Chelsea’s fortunes after they first tried to sign me," he added. "I developed a bit of a soft spot for the club.
"The problem was that Shakhtar didn’t want to let me go and then Anzhi came in and met my release clause fee.
"But that made my desire to play for Chelsea all the stronger. It took a while, but now I’m here, and I couldn’t be happier.
"My life changed a lot [in 2013]. But it was a great year too, and I’m really happy where I am right now."