Mata opened the scoring in a 3-1 win for Rafael Benitez's men that sets up a meeting with Corinthians of Brazil in Sunday's showpiece match in Japan.
Mata's 11th goal of the season gave the European champions the edge at the interval, and three minutes into the second period they were three goals to the good thanks to a Fernando Torres strike and a Darvin Chavez own goal.
A group of travelling Chelsea fans cheered on their team at a half-empty Nissan Stadium in Yokohama, and Mata has vowed to put on a show this weekend as the Blues bid to be crowned the top club side in world football.
"I'm so glad today, the way that we won," Mata said aftwards.
"For us it is a very important tournament, we want to win this trophy, to be world champions and on Sunday we will try our best to win.
"I'm very happy with my goal. In the second half we started really well, we were really focused on scoring more goals and we did it with Fernando and the own goal, so 3-1 is a good result for us."
Looking ahead to Sunday's final, the Spain international added: "We have confidence but we know that Corinthians are a really good team, one of the best in South America.
"They have a lot of supporters here with them but we have our supporters as well and it will be a football party and hopefully we will win."