The Dutch striker opened his scoring account for Spurs with a well-taken second-half penalty at White Hart Lane on Wednesday night.
Janssen's maiden goal for the North London club comes at a good time as star striker Harry Kane is sidelined with an ankle injury and Pochettino highlighted the importance of the summer signing gaining confidence from a scoring display.
"Now that Harry Kane's injured, he is our main striker and it's important for his confidence for the next few games," Pochettino said.
"Always I allow them to take the ball and whoever feels more confidence to shoot, but I remember in the national team against England he took the ball and took the penalty.
"I think that it was important for him, to feel the love from the supporters.
"For a striker, always the difficult thing is to create chances but he has a lot of chances to score today. He was unlucky.
"The important thing is that he got into the box and he created a lot of chances. For the future, it's important that he feels confidence and for the team, it will help a lot for us."