Janssen only scored six times while at Spurs but netted his side's second from the penalty spot in Saturday's explosive Istanbul derby.
Five players were sent off, including former Chelsea loanee Ricardo Quaresma, as Janssen's penalty proved to be the winner in a 2-1 victory over Besiktas.
"My transfer to Fenerbahce has been a kind of salvation," Janssen told reporters.
"If you get this opportunity, you're grateful [to the people who gave it to you]. It's nice to get minutes here and you'll take that chance with both hands.
"I really enjoyed my first Istanbul derby. The atmosphere was fantastic with the passion of the supporters. I have never experienced anything like this before. A lot happened in the game - five red cards in particular."
Fenerbahce face a trip to Akhisar on Friday before hosting Yeni Malatyaspor on October 15.