The 24-year-old joined Chelsea from Valencia in 2011 and hit the ground running with a string of impressive performances, but the Spanish playmaker has admitted that he was surprised with how well he performed during his first season in England.
Mata told France Football: "To be honest, I didn't expect it. It was my first season in England and everything came quickly.
"I immediately found my mark, thanks to my teammates. I was lucky to score a goal in my very first match. Then, I had fun.
"I came to Chelsea because I wanted to win trophies, and in my first season, I got two, notably the first Champions League in the club's history."
Mata has already scored four goals in 10 Chelsea appearances this season.