The 25-year-old says there is plenty more to come from him now that he is up and running.
Willian told Globo Esporte: "I am very happy to have made my Premier League debut this way.
"I did well off the bench, doing what Mourinho asked me to do. I managed to start the move that led to the second goal and then I scored the third goal.
"It was very exciting and I am not only happy for the goal, but also for the win - which was important for our team.
"I am slowly recovering my best form, gaining match fitness.
"I will try to do my best whenever I have the opportunity to play. I intend to grow with each match."
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