Pochettino told BT Sport: "It was so important to win, we are so happy. It was so important to start well in a tough game. Dortmund played really well, they dominated the first half. We increased our level in the second half and we were very clinical in front of goal.
"It is more than three points. At half-time we fixed some problems and modified the position of some players. The tempo of the game decreased which was better for us. Dortmund are a very aggressive team, we struggled a little to pass the ball quickly.
"Sometimes you can't dominate, you have to play a different way and the team is more mature now. We can learn a lot from this game."
The win puts Tottenham joint-top of the Group H standings alongside Real Madrid, who were victorious at home to APOEL.