Goals from Andriy Shevchenko and substitute Shaun Wright-Phillips sealed a workmanlike victory that made sure Chelsea finished top of Group A ahead of holders Barcelona.
Mourinho, whose side were keeping plenty in reserve for Sunday's home game with Arsenal and a hectic festive schedule, told a news conference: "I know football, I know players' mentality. I know when you just need to finish a job -- and that was a perfect example.
"We knew we just needed three points to be top of the group and at halftime we knew the score in Barcelona (2-0 ahead of Werder Bremen), so we knew that we just needed a point.
"We were 1-0 up and we have a big month ahead of us, so I think the players just controlled their emotions and the game. They didn't play to their maximum -- and I didn't demand a lot.
"The game was quite easy and played in an easy way. It was almost like a friendly."
As for Shevchenko, who scored his first Champions League goal for Chelsea and only his fifth of the season since a 30 million pounds ($59.30 million) move from AC Milan, he said: "I'm happy with Sheva. It's only one goal for us in the Champions League but hopefully in the knockout stage he has some more to help us to go further in the competition."
Mourinho was also pleased for Wright-Phillips, the subject of recent transfer speculation after failing to establish himself in the first team since joining the club in 2005.
"Normally, I don't care about who the goalscorer is, but he's a special case," Mourinho said. "It's his first official goal for Chelsea and he's a boy who deserves to be happy."
Levski coach Stanimir Stoilov, whose side were Bulgaria's first to make the group phase of the Champions League, was upbeat despite recording a sixth defeat in their six games.
"It was a good match -- Chelsea were better and deserved to win," hw said. "We tried to play good football and do our best, and for most of the time we were equal. But the better team won."
As for being in Europe's top club competition, he said: "It was a long-awaited moment for Bulgarian football and I'm glad it was our team who achieved it ... It was good experience.
"We are still a bit naive but we'll learn our lessons and I hope we'll improve next year."
