The midfielder, who was a target for Barcelona, insists he is relishing the prospect of working under a coach of the Special One's immense standing and calibre.
Mata, 25 said: "I met with Jose on my first day in training. I think he's a great manager who did a really great job the last time he was here.
"The break was really good for me. I had time to rest and disconnect from football - but now I am back at Chelsea and really looking forward to the new season.
"I'm really excited about it and I'm very happy to be here."