Mata scored on his Blues debut in victory over Norwich City last night.
Asked how he felt about the transfer, Torres told Chelsea TV he was delighted to see his international colleague join the club.
"It's great news, I've been playing with him a long time in the national team and I know him very well," said the 27-year-old. "As soon as I knew Chelsea showed some interest in him I was sending him texts and talking almost every day. He had other offers from different clubs because he's a great player, but from the first day he told me he wanted to come to Chelsea.
"I know what he can bring to the team, and I think he is going to be a great player for us. As soon as he is involved in the routine of the team it won't be a problem to change from Spanish to English football, because a player like him with his quality and sharpness will find it easy.
"It's great news for Chelsea who have signed two great young players but with the experience to play in the Premier League. Hopefully that can help Oriol be very soon in the national team.
"I'm trying to help them the same as the players that were here when I arrived helped me, and I'm trying to help with the small things you need in a new city and a new country because it's not easy."