Niittymäki was the Philadelphia Flyers' 6th round pick (168th overall) in the 1998 NHL Entry Draft. "I didn't even know I got drafted. I found out the next morning. I was really surprised," he said in an interview in November 2003. Even if he had opted to go immediately to the United States to play hockey, compulsory military service kept Niittymäki in Finland until January 2001. He would return to TPS in 2012 for his final season, playing 14 games.